experiment for electromagnetic induction

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In this hands-on electronics experiment, you will learn about electromagnetic induction using an electromagnet and a permanent magnet.

Project overview.

Electromagnetic induction is a complementary phenomenon to electromagnetism . Instead of producing a magnetic field from electricity, we produce electricity from a magnetic field. There is one important difference, though, whereas electromagnetism produces a steady magnetic field from a steady electric current, electromagnetic induction requires motion between the magnet and the coil to produce a voltage . In this project, you measure electromagnetic induction using the test setup illustrated in Figure 1.

Figure 1. Circuit for measuring the induced voltage from the electromagnet.

Parts and materials.

• Electromagnet from the previous project:  building an electromagnet
• Permanent magnet

Learning Objectives

• Relationship between magnetic field strength and induced voltage

Instructions

Step 1:  Connect the multimeter to the coil, as illustrated in Figures 1 and 2, and set it to the most sensitive DC voltage range available. 

Figure 2.  The schematic diagram for measuring the induced voltage from the electromagnet.

If you are using an analog multimeter , be sure to use long jumper wires and locate the meter far away from the coil, as the magnetic field from the permanent magnet may affect the meter’s operation and produce false readings. Digital meters are unaffected by magnetic fields.

Step 2:  Measure the voltage output from the electromagnet. Hint: it should be zero! 

Step 3:  Move the magnet slowly to and from one end of the electromagnet, noting the polarity and magnitude of the induced voltage.

Step 4:  Experiment with moving the magnet, and discover for yourself what factor(s) determine the amount of voltage induced. Consider the distance from the electromagnet and speed of movement.

Step 5:  Repeat the process at the other end of the electromagnet coil and compare results.

Step 6: Repeat the process using the other end of the permanent magnet and compare.

Related Content

Learn more about the fundamentals behind this project in the resources below.

• Magnetism and Electromagnetism
• Electromagnetism

Worksheets:

• Basic Electromagnetism and Electromagnetic Induction Worksheet
• Intermediate Electromagnetism and Electromagnetic Induction Worksheet
• Advanced Electromagnetism and Electromagnetic Induction Worksheet
• Textbook Index
• Back To Index

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20.3 Electromagnetic Induction

Section learning objectives.

By the end of this section, you will be able to do the following:

• Explain how a changing magnetic field produces a current in a wire
• Calculate induced electromotive force and current

Teacher Support

The learning objectives in this section will help your students master the following standards:

• (G) investigate and describe the relationship between electric and magnetic fields in applications such as generators, motors, and transformers.

In addition, the OSX High School Physics Laboratory Manual addresses content in this section in the lab titled: Magnetism, as well as the following standards:

Section Key Terms

Changing Magnetic Fields

In the preceding section, we learned that a current creates a magnetic field. If nature is symmetrical, then perhaps a magnetic field can create a current. In 1831, some 12 years after the discovery that an electric current generates a magnetic field, English scientist Michael Faraday (1791–1862) and American scientist Joseph Henry (1797–1878) independently demonstrated that magnetic fields can produce currents. The basic process of generating currents with magnetic fields is called induction ; this process is also called magnetic induction to distinguish it from charging by induction, which uses the electrostatic Coulomb force.

When Faraday discovered what is now called Faraday’s law of induction, Queen Victoria asked him what possible use was electricity. “Madam,” he replied, “What good is a baby?” Today, currents induced by magnetic fields are essential to our technological society. The electric generator—found in everything from automobiles to bicycles to nuclear power plants—uses magnetism to generate electric current. Other devices that use magnetism to induce currents include pickup coils in electric guitars, transformers of every size, certain microphones, airport security gates, and damping mechanisms on sensitive chemical balances.

One experiment Faraday did to demonstrate magnetic induction was to move a bar magnet through a wire coil and measure the resulting electric current through the wire. A schematic of this experiment is shown in Figure 20.33 . He found that current is induced only when the magnet moves with respect to the coil. When the magnet is motionless with respect to the coil, no current is induced in the coil, as in Figure 20.33 . In addition, moving the magnet in the opposite direction (compare Figure 20.33 with Figure 20.33 ) or reversing the poles of the magnet (compare Figure 20.33 with Figure 20.33 ) results in a current in the opposite direction.

Virtual Physics

Faraday’s law.

Try this simulation to see how moving a magnet creates a current in a circuit. A light bulb lights up to show when current is flowing, and a voltmeter shows the voltage drop across the light bulb. Try moving the magnet through a four-turn coil and through a two-turn coil. For the same magnet speed, which coil produces a higher voltage?

• The sign of voltage will change because the direction of current flow will change by moving south pole of the magnet to the left.
• The sign of voltage will remain same because the direction of current flow will not change by moving south pole of the magnet to the left.
• The sign of voltage will change because the magnitude of current flow will change by moving south pole of the magnet to the left.
• The sign of voltage will remain same because the magnitude of current flow will not change by moving south pole of the magnet to the left.

Induced Electromotive Force

If a current is induced in the coil, Faraday reasoned that there must be what he called an electromotive force pushing the charges through the coil. This interpretation turned out to be incorrect; instead, the external source doing the work of moving the magnet adds energy to the charges in the coil. The energy added per unit charge has units of volts, so the electromotive force is actually a potential. Unfortunately, the name electromotive force stuck and with it the potential for confusing it with a real force. For this reason, we avoid the term electromotive force and just use the abbreviation emf , which has the mathematical symbol ε . ε . The emf may be defined as the rate at which energy is drawn from a source per unit current flowing through a circuit. Thus, emf is the energy per unit charge added by a source, which contrasts with voltage, which is the energy per unit charge released as the charges flow through a circuit.

To understand why an emf is generated in a coil due to a moving magnet, consider Figure 20.34 , which shows a bar magnet moving downward with respect to a wire loop. Initially, seven magnetic field lines are going through the loop (see left-hand image). Because the magnet is moving away from the coil, only five magnetic field lines are going through the loop after a short time Δ t Δ t (see right-hand image). Thus, when a change occurs in the number of magnetic field lines going through the area defined by the wire loop, an emf is induced in the wire loop. Experiments such as this show that the induced emf is proportional to the rate of change of the magnetic field. Mathematically, we express this as

where Δ B Δ B is the change in the magnitude in the magnetic field during time Δ t Δ t and A is the area of the loop.

Note that magnetic field lines that lie in the plane of the wire loop do not actually pass through the loop, as shown by the left-most loop in Figure 20.35 . In this figure, the arrow coming out of the loop is a vector whose magnitude is the area of the loop and whose direction is perpendicular to the plane of the loop. In Figure 20.35 , as the loop is rotated from θ = 90° θ = 90° to θ = 0° , θ = 0° , the contribution of the magnetic field lines to the emf increases. Thus, what is important in generating an emf in the wire loop is the component of the magnetic field that is perpendicular to the plane of the loop, which is B cos θ . B cos θ .

This is analogous to a sail in the wind. Think of the conducting loop as the sail and the magnetic field as the wind. To maximize the force of the wind on the sail, the sail is oriented so that its surface vector points in the same direction as the winds, as in the right-most loop in Figure 20.35 . When the sail is aligned so that its surface vector is perpendicular to the wind, as in the left-most loop in Figure 20.35 , then the wind exerts no force on the sail.

Thus, taking into account the angle of the magnetic field with respect to the area, the proportionality E ∝ Δ B / Δ t E ∝ Δ B / Δ t becomes

Another way to reduce the number of magnetic field lines that go through the conducting loop in Figure 20.35 is not to move the magnet but to make the loop smaller. Experiments show that changing the area of a conducting loop in a stable magnetic field induces an emf in the loop. Thus, the emf produced in a conducting loop is proportional to the rate of change of the product of the perpendicular magnetic field and the loop area

where B cos θ B cos θ is the perpendicular magnetic field and A is the area of the loop. The product B A cos θ B A cos θ is very important. It is proportional to the number of magnetic field lines that pass perpendicularly through a surface of area A . Going back to our sail analogy, it would be proportional to the force of the wind on the sail. It is called the magnetic flux and is represented by Φ Φ .

The unit of magnetic flux is the weber (Wb), which is magnetic field per unit area, or T/m 2 . The weber is also a volt second (Vs).

The induced emf is in fact proportional to the rate of change of the magnetic flux through a conducting loop.

Finally, for a coil made from N loops, the emf is N times stronger than for a single loop. Thus, the emf induced by a changing magnetic field in a coil of N loops is

The last question to answer before we can change the proportionality into an equation is “In what direction does the current flow?” The Russian scientist Heinrich Lenz (1804–1865) explained that the current flows in the direction that creates a magnetic field that tries to keep the flux constant in the loop. For example, consider again Figure 20.34 . The motion of the bar magnet causes the number of upward-pointing magnetic field lines that go through the loop to decrease. Therefore, an emf is generated in the loop that drives a current in the direction that creates more upward-pointing magnetic field lines. By using the right-hand rule, we see that this current must flow in the direction shown in the figure. To express the fact that the induced emf acts to counter the change in the magnetic flux through a wire loop, a minus sign is introduced into the proportionality ε ∝ Δ Φ / Δ t . ε ∝ Δ Φ / Δ t . , which gives Faraday’s law of induction.

Lenz’s law is very important. To better understand it, consider Figure 20.36 , which shows a magnet moving with respect to a wire coil and the direction of the resulting current in the coil. In the top row, the north pole of the magnet approaches the coil, so the magnetic field lines from the magnet point toward the coil. Thus, the magnetic field B → mag = B mag ( x ^ ) B → mag = B mag ( x ^ ) pointing to the right increases in the coil. According to Lenz’s law, the emf produced in the coil will drive a current in the direction that creates a magnetic field B → coil = B coil ( − x ^ ) B → coil = B coil ( − x ^ ) inside the coil pointing to the left. This will counter the increase in magnetic flux pointing to the right. To see which way the current must flow, point your right thumb in the desired direction of the magnetic field B → coil, B → coil, and the current will flow in the direction indicated by curling your right fingers. This is shown by the image of the right hand in the top row of Figure 20.36 . Thus, the current must flow in the direction shown in Figure 4(a) .

In Figure 4(b) , the direction in which the magnet moves is reversed. In the coil, the right-pointing magnetic field B → mag B → mag due to the moving magnet decreases. Lenz’s law says that, to counter this decrease, the emf will drive a current that creates an additional right-pointing magnetic field B → coil B → coil in the coil. Again, point your right thumb in the desired direction of the magnetic field, and the current will flow in the direction indicate by curling your right fingers ( Figure 4(b) ).

Finally, in Figure 4(c) , the magnet is reversed so that the south pole is nearest the coil. Now the magnetic field B → mag B → mag points toward the magnet instead of toward the coil. As the magnet approaches the coil, it causes the left-pointing magnetic field in the coil to increase. Lenz’s law tells us that the emf induced in the coil will drive a current in the direction that creates a magnetic field pointing to the right. This will counter the increasing magnetic flux pointing to the left due to the magnet. Using the right-hand rule again, as indicated in the figure, shows that the current must flow in the direction shown in Figure 4(c) .

Faraday’s Electromagnetic Lab

This simulation proposes several activities. For now, click on the tab Pickup Coil, which presents a bar magnet that you can move through a coil. As you do so, you can see the electrons move in the coil and a light bulb will light up or a voltmeter will indicate the voltage across a resistor. Note that the voltmeter allows you to see the sign of the voltage as you move the magnet about. You can also leave the bar magnet at rest and move the coil, although it is more difficult to observe the results.

• Yes, the current in the simulation flows as shown because the direction of current is opposite to the direction of flow of electrons.
• No, current in the simulation flows in the opposite direction because the direction of current is same to the direction of flow of electrons.

Watch Physics

Induced current in a wire.

This video explains how a current can be induced in a straight wire by moving it through a magnetic field. The lecturer uses the cross product , which a type of vector multiplication. Don’t worry if you are not familiar with this, it basically combines the right-hand rule for determining the force on the charges in the wire with the equation F = q v B sin θ . F = q v B sin θ .

Grasp Check

What emf is produced across a straight wire 0.50 m long moving at a velocity of (1.5 m/s) x ^ x ^ through a uniform magnetic field (0.30 T) ẑ ? The wire lies in the ŷ -direction. Also, which end of the wire is at the higher potential—let the lower end of the wire be at y = 0 and the upper end at y = 0.5 m)?

• 0.15 V and the lower end of the wire will be at higher potential
• 0.15 V and the upper end of the wire will be at higher potential
• 0.075 V and the lower end of the wire will be at higher potential
• 0.075 V and the upper end of the wire will be at higher potential

Worked Example

Emf induced in conducing coil by moving magnet.

Imagine a magnetic field goes through a coil in the direction indicated in Figure 20.37 . The coil diameter is 2.0 cm. If the magnetic field goes from 0.020 to 0.010 T in 34 s, what is the direction and magnitude of the induced current? Assume the coil has a resistance of 0.1 Ω. Ω.

Use the equation ε = − N Δ Φ / Δ t ε = − N Δ Φ / Δ t to find the induced emf in the coil, where Δ t = 34 s Δ t = 34 s . Counting the number of loops in the solenoid, we find it has 16 loops, so N = 16 . N = 16 . Use the equation Φ = B A cos θ Φ = B A cos θ to calculate the magnetic flux

where d is the diameter of the solenoid and we have used cos 0° = 1 . cos 0° = 1 . Because the area of the solenoid does not vary, the change in the magnetic of the flux through the solenoid is

Once we find the emf, we can use Ohm’s law, ε = I R , ε = I R , to find the current.

Finally, Lenz’s law tells us that the current should produce a magnetic field that acts to oppose the decrease in the applied magnetic field. Thus, the current should produce a magnetic field to the right.

Combining equations ε = − N Δ Φ / Δ t ε = − N Δ Φ / Δ t and Φ = B A cos θ Φ = B A cos θ gives

Solving Ohm’s law for the current and using this result gives

Lenz’s law tells us that the current must produce a magnetic field to the right. Thus, we point our right thumb to the right and curl our right fingers around the solenoid. The current must flow in the direction in which our fingers are pointing, so it enters at the left end of the solenoid and exits at the right end.

Let’s see if the minus sign makes sense in Faraday’s law of induction. Define the direction of the magnetic field to be the positive direction. This means the change in the magnetic field is negative, as we found above. The minus sign in Faraday’s law of induction negates the negative change in the magnetic field, leaving us with a positive current. Therefore, the current must flow in the direction of the magnetic field, which is what we found.

Now try defining the positive direction to be the direction opposite that of the magnetic field, that is positive is to the left in Figure 20.37 . In this case, you will find a negative current. But since the positive direction is to the left, a negative current must flow to the right, which again agrees with what we found by using Lenz’s law.

Magnetic Induction due to Changing Circuit Size

The circuit shown in Figure 20.38 consists of a U-shaped wire with a resistor and with the ends connected by a sliding conducting rod. The magnetic field filling the area enclosed by the circuit is constant at 0.01 T. If the rod is pulled to the right at speed v = 0.50 m/s, v = 0.50 m/s, what current is induced in the circuit and in what direction does the current flow?

We again use Faraday’s law of induction, E = − N Δ Φ Δ t , E = − N Δ Φ Δ t , although this time the magnetic field is constant and the area enclosed by the circuit changes. The circuit contains a single loop, so N = 1 . N = 1 . The rate of change of the area is Δ A Δ t = v ℓ . Δ A Δ t = v ℓ . Thus the rate of change of the magnetic flux is

where we have used the fact that the angle θ θ between the area vector and the magnetic field is 0°. Once we know the emf, we can find the current by using Ohm’s law. To find the direction of the current, we apply Lenz’s law.

Faraday’s law of induction gives

Solving Ohm’s law for the current and using the previous result for emf gives

As the rod slides to the right, the magnetic flux passing through the circuit increases. Lenz’s law tells us that the current induced will create a magnetic field that will counter this increase. Thus, the magnetic field created by the induced current must be into the page. Curling your right-hand fingers around the loop in the clockwise direction makes your right thumb point into the page, which is the desired direction of the magnetic field. Thus, the current must flow in the clockwise direction around the circuit.

Is energy conserved in this circuit? An external agent must pull on the rod with sufficient force to just balance the force on a current-carrying wire in a magnetic field—recall that F = I ℓ B sin θ . F = I ℓ B sin θ . The rate at which this force does work on the rod should be balanced by the rate at which the circuit dissipates power. Using F = I ℓ B sin θ , F = I ℓ B sin θ , the force required to pull the wire at a constant speed v is

where we used the fact that the angle θ θ between the current and the magnetic field is 90° . 90° . Inserting our expression above for the current into this equation gives

The power contributed by the agent pulling the rod is F pull v , or F pull v , or

The power dissipated by the circuit is

We thus see that P pull + P dissipated = 0 , P pull + P dissipated = 0 , which means that power is conserved in the system consisting of the circuit and the agent that pulls the rod. Thus, energy is conserved in this system.

Practice Problems

The magnetic flux through a single wire loop changes from 3.5 Wb to 1.5 Wb in 2.0 s. What emf is induced in the loop?

What is the emf for a 10-turn coil through which the flux changes at 10 Wb/s?

Check Your Understanding

• An electric current is induced if a bar magnet is placed near the wire loop.
• An electric current is induced if a wire loop is wound around the bar magnet.
• An electric current is induced if a bar magnet is moved through the wire loop.
• An electric current is induced if a bar magnet is placed in contact with the wire loop.
• Induced current can be created by changing the size of the wire loop only.
• Induced current can be created by changing the orientation of the wire loop only.
• Induced current can be created by changing the strength of the magnetic field only.
• Induced current can be created by changing the strength of the magnetic field, changing the size of the wire loop, or changing the orientation of the wire loop.

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Science project, electromagnetic induction experiment.

Electricity is carried by current , or the flow of electrons. One useful characteristic of current is that it creates its own magnetic field. This is useful in many types of motors and appliances. Conduct this simple electromagnetic induction experiment to witness this phenomenon for yourself!

Observe how current can create a magnetic field.

What will happen when the battery is connected and the switch is turned on? Will the battery voltage make a difference in the magnetic field?

• Thin copper wire
• Long metal nail
• 12-V lantern battery
• 9-V battery
• Wire cutters
• Toggle switch
• Electrical tape
• Paper clips
• Cut a long length of wire and attached one end to the positive output of the toggle switch.
• Twist the wire at least 50 times around the nail to create a solenoid.
• Once the wire has covered the nail, tape the wire to the negative terminal of the 12V battery.
• Cut a short piece of wire to connect the positive terminal of the battery to the negative terminal of the toggle switch.

• Turn on the switch.
• Bring paper clips close to the nail. What happens? How many paper clips can you pick up?
• Repeat the experiment with the 9V battery.
• Repeat the experiment with the 9V and 12V batteries arranged in series (if you don’t know how to arrange batteries in series, check out this project that explains how).

The current running through the circuit will cause the nail to be magnetic and attract paper clips. The 12V battery will create a stronger magnet than the 9V battery. The series circuit will create a stronger magnet than the individual batteries did.

Electric currents always produce their own magnetic fields. This phenomenon is represented by the right-hand-rule:

If you make the “Thumbs-Up” sign with your hand like this:

The current will flow in the direction the thumb is pointing, and the magnetic field direction will be described by the direction of the fingers. This means when you change the direction of the current, you also change the direction of the magnetic field. Current flows (which means electrons flow) from the negative end of a battery through the wire to the positive end of the battery, which can help you determine what the direction of the magnetic field will be.

When the toggle switch is turned on, the current will flow from the negative terminal of the battery around the circuit to the positive terminal. When the current passes through the nail it induces , or creates, a magnetic field.  The 12V battery produces a larger voltage ; therefore, produces a higher current for a circuit of the same resistance. Larger currents will induce larger (and stronger!) magnetic fields, so the nail will attract more paperclips when using a larger voltage.

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Faraday, the greatest experimentalist in electricity and magnetism of the 19th century and one of the greatest experimental physicists of all time, worked on and off for 10 years trying to prove that a magnet could induce electricity. In 1831 he finally succeeded by using two coils of wire wound around opposite sides of a ring of soft iron ( Figure 7 ). The first coil was attached to a battery; when a current passed through the coil, the iron ring became magnetized. A wire from the second coil was extended to a compass needle a metre away, far enough so that it was not affected directly by any current in the first circuit . When the first circuit was turned on, Faraday observed a momentary deflection of the compass needle and its immediate return to its original position. When the primary current was switched off, a similar deflection of the compass needle occurred but in the opposite direction. Building on this observation in other experiments, Faraday showed that changes in the magnetic field around the first coil are responsible for inducing the current in the second coil. He also demonstrated that an electric current can be induced by moving a magnet, by turning an electromagnet on and off, and even by moving an electric wire in Earth’s magnetic field . Within a few months, Faraday built the first, albeit primitive, electric generator .

Henry had discovered electric induction quite independently in 1830, but his results were not published until after he had received news of Faraday’s 1831 work , nor did he develop the discovery as fully as Faraday. In his paper of July 1832, Henry reported and correctly interpreted self-induction . He had produced large electric arcs from a long helical conductor when it was disconnected from a battery. When he had opened the circuit, the rapid decrease in the current had caused a large voltage between the battery terminal and the wire. As the wire lead was pulled away from the battery, the current continued to flow for a short time in the form of a bright arc between the battery terminal and the wire.

Faraday’s thinking was permeated by the concept of electric and magnetic lines of force . He visualized that magnets, electric charges, and electric currents produce lines of force. When he placed a thin card covered with iron filings on a magnet, he could see the filings form chains from one end of the magnet to the other. He believed that these lines showed the directions of the forces and that electric current would have the same lines of force. The tension they build explains the attraction and repulsion of magnets and electric charges. Faraday had visualized magnetic curves as early as 1831 while working on his induction experiments; he wrote in his notes, “By magnetic curves I mean lines of magnetic forces which would be depicted by iron filings.” Faraday opposed the prevailing idea that induction occurred “at a distance”; instead, he held that induction occurs along curved lines of force because of the action of contiguous particles. Later he explained that electricity and magnetism are transmitted through a medium that is the site of electric or magnetic “fields,” which make all substances magnetic to some extent.

Faraday was not the only researcher laying the groundwork for a synthesis between electricity, magnetism, and other areas of physics . On the continent of Europe , primarily in Germany , scientists were making mathematical connections between electricity, magnetism, and optics . The work of the physicists Franz Ernst Neumann , Wilhelm Eduard Weber , and H.F.E. Lenz belongs to this period. At the same time, Helmholtz and the English physicists William Thomson (later Lord Kelvin) and James Prescott Joule were clarifying the relationship between electricity and other forms of energy . Joule investigated the quantitative relationship between electric currents and heat during the 1840s and formulated the theory of the heating effects that accompany the flow of electricity in conductors. Helmholtz, Thomson, Henry, Gustav Kirchhoff , and Sir George Gabriel Stokes also extended the theory of the conduction and propagation of electric effects in conductors. In 1856 Weber and his German colleague, Rudolf Kohlrausch , determined the ratio of electric and magnetic units and found that it has the same dimensions as light and that it is almost exactly equal to its velocity . In 1857 Kirchhoff used this finding to demonstrate that electric disturbances propagate on a highly conductive wire with the speed of light .

The final steps in synthesizing electricity and magnetism into one coherent theory were made by Maxwell. He was deeply influenced by Faraday’s work, having begun his study of the phenomena by translating Faraday’s experimental findings into mathematics. (Faraday was self-taught and had never mastered mathematics .) In 1856 Maxwell developed the theory that the energy of the electromagnetic field is in the space around the conductors as well as in the conductors themselves. By 1864 he had formulated his own electromagnetic theory of light, predicting that both light and radio waves are electric and magnetic phenomena. While Faraday had discovered that changes in magnetic fields produce electric fields , Maxwell added the converse: changes in electric fields produce magnetic fields even in the absence of electric currents. Maxwell predicted that electromagnetic disturbances traveling through empty space have electric and magnetic fields at right angles to each other and that both fields are perpendicular to the direction of the wave . He concluded that the waves move at a uniform speed equal to the speed of light and that light is one form of electromagnetic wave . Their elegance notwithstanding, Maxwell’s radical ideas were accepted by few outside England until 1886, when the German physicist Heinrich Hertz verified the existence of electromagnetic waves traveling at the speed of light; the waves he discovered are known now as radio waves .

Maxwell’s four field equations represent the pinnacle of classical electromagnetic theory. Subsequent developments in the theory have been concerned either with the relationship between electromagnetism and the atomic structure of matter or with the practical and theoretical consequences of Maxwell’s equations . His formulation has withstood the revolutions of relativity and quantum mechanics . His equations are appropriate for distances as small as 10 −10 centimetres —100 times smaller than the size of an atom . The fusion of electromagnetic theory and quantum theory, known as quantum electrodynamics , is required only for smaller distances.

While the mainstream of theoretical activity concerning electric and magnetic phenomena during the 19th century was devoted to showing how they are interrelated, some scientists made use of them to discover new properties of materials and heat. Weber developed Ampère’s suggestion that there are internal circulating currents of molecular size in metals. He explained how a substance loses its magnetic properties when the molecular magnets point in random directions. Under the action of an external force, they may turn to point in the direction of the force; when all point in this direction, the maximum possible degree of magnetization is reached, a phenomenon known as magnetic saturation . In 1895 Pierre Curie of France discovered that a ferromagnetic substance has a specific temperature above which it ceases to be magnetic. Finally, superconductivity was discovered in 1900 by the German physicist Heike Kammerlingh-Onnes. In superconductivity , electric conductors lose all resistance at very low temperatures .

Although little of major importance was added to electromagnetic theory in the 19th century after Maxwell, the discovery of the electron in 1898 opened up an entirely new area of study: the nature of electric charge and of matter itself. The discovery of the electron grew out of studies of electric currents in vacuum tubes . Heinrich Geissler , a glassblower who assisted the German physicist Julius Plücker , improved the vacuum tube in 1854. Four years later, Plücker sealed two electrodes inside the tube, evacuated the air, and forced electric currents between the electrodes; he attributed the green glow that appeared on the wall of the tube to rays emanating from the cathode . From then until the end of the century, the properties of cathode-ray discharges were studied intensively. The work of the English physicist Sir William Crookes in 1879 indicated that the luminescence was a property of the electric current itself. Crookes concluded that the rays were composed of electrified charged particles. In 1898 another English physicist, Sir J.J. Thomson , identified a cathode ray as a stream of negatively charged particles, each having a mass 1 / 1836 smaller than that of a hydrogen ion . Thomson’s discovery established the particulate nature of charge; his particles were later dubbed electrons .

Following the discovery of the electron, electromagnetic theory became an integral part of the theories of the atomic, subatomic, and subnuclear structure of matter. This shift in focus occurred as the result of an impasse between electromagnetic theory and statistical mechanics over attempts to understand radiation from hot bodies. Thermal radiation had been investigated in Germany by the physicist Wilhelm Wien between 1890 and 1900. Wien had virtually exhausted the resources of thermodynamics in dealing with this problem. Two British scientists, Lord Rayleigh (John William Strutt) and Sir James Hopwood Jeans , had by 1900 applied the newly developed science of statistical mechanics to the same problem. They obtained results that, though in agreement with Wien’s thermodynamic conclusions (as distinct from his speculative extensions of thermodynamics ), only partially agreed with experimental observations. The German physicist Max Planck attempted to combine the statistical approach with a thermodynamic approach. By concentrating on the necessity of fitting together the experimental data, he was led to the formulation of an empirical law that satisfied Wien’s thermodynamic criteria and accommodated the experimental data. When Planck interpreted this law in terms of Rayleigh’s statistical concepts, he concluded that radiation of frequency ν exists only in quanta of energy. Planck’s result, including the introduction of the new universal constant h in 1900, marked the foundation of quantum mechanics and initiated a profound change in physical theory ( see atom: Bohr’s shell model ).

By 1900 it was apparent that Thomson’s electrons were a universal constituent of matter and, thus, that matter is essentially electric in nature. As a result, in the early years of the 20th century, many physicists attempted to construct theories of the electromagnetic properties of metals , insulators , and magnetic materials in terms of electrons. In 1909 the Dutch physicist Hendrik Antoon Lorentz succeeded in doing so in The Theory of Electrons and Its Applications to the Phenomena of Light and Radiant Heat ; his work has since been modified by quantum theory.

Project On Electromagnetic Induction For Class 12th

Table of Contents

Introduction

Electromagnetic induction, a cornerstone of modern electrical engineering, is more than just a concept; it’s a force that powers our daily lives and drives our technological marvels. In this journey, we’ll unravel the essence of electromagnetic induction and its indispensable role in the world of technology.

Historical Perspective

Let’s take a leap into the past, where visionaries like Michael Faraday and Heinrich Lenz laid the foundation for our understanding of electromagnetic induction. Their pioneering experiments unveiled the profound connection between electricity and magnetism.

Michael Faraday: In the early 19th century, the brilliant British scientist Michael Faraday embarked on groundbreaking experiments. His work with coils of wire and magnets revealed the extraordinary: a changing magnetic field could spark an electric current in nearby conductors. This revelation was a seismic shift, paving the way for the development of electric generators.

Heinrich Lenz: In 1834, Russian physicist Heinrich Lenz formulated Lenz’s Law. This law states that the direction of an induced current opposes the change in magnetic flux that produced it. Lenz’s Law stands as a fundamental rule in determining the direction of induced currents, ensuring that energy remains conserved within electromagnetic systems.

Principles of Electromagnetic Induction

Now, we delve into the core principles that govern electromagnetic induction. At center stage is Faraday’s Law, the beacon that illuminates how a changing magnetic field conjures an electromotive force (emf).

Faraday’s Law of Electromagnetic Induction: This law states that the electromotive force (emf) induced in a closed circuit is directly proportional to the rate of change of magnetic flux passing through it. In mathematical terms:

• emf is the electromotive force (in volts).
• N is the number of turns in the coil.
• dΦ/dt is the rate of change of magnetic flux (in webers per second, Wb/s).

This law forms the bedrock of electromagnetic induction, binding the dynamics of magnetic fields to the generation of electrical current.

Lenz’s Law

Lenz’s Law emerges as the guiding star for discerning the direction of induced currents. Through practical examples and visual demonstrations, we demystify the concept of self-consistency in electromagnetic induction.

Lenz’s Law: This principle declares that the direction of an induced current in a closed loop opposes the change in magnetic flux that gave birth to it. Lenz’s Law safeguards the conservation of energy, ensuring that electromagnetic systems abide by the laws of physics.

Imagine this scenario: Picture a coil of wire as you move a magnet closer to it. As the magnet nears the coil, it ushers in an increasing magnetic flux. Lenz’s Law steps in, dictating that an induced current will flow through the coil in a manner that counteracts the magnet’s motion. The coil acts as a magnetic brake, resisting the magnet’s advance.

Lenz’s Law is the guardian of electromagnetic induction, preserving the sanctity of energy conservation.

Factors Affecting Induced emf

Let’s dissect the magnitude of induced emf, diving into the factors that influence it. We’ll navigate the subtleties of magnetic flux, coil turns, and their intricate dance with induced emf.

Factors Affecting Induced emf: Several variables sway the magnitude of induced electromotive force (emf) in a conductor:

• Rate of Change of Magnetic Flux: The faster the magnetic field transforms, the greater the induced emf. This aligns seamlessly with Faraday’s Law, which links emf directly to the rate of flux change.
• Number of Turns in the Coil: An upsurge in the number of coil turns (N) augments the induced emf. Each coil turn contributes to the overall emf, making coil geometry a pivotal factor.
• Strength of the Magnetic Field: A robust magnetic field begets a more substantial emf. The relationship between magnetic field strength and induced emf follows a linear path.
• Angle Between Magnetic Field and Coil: The angle formed between the magnetic field and the coil plays a role in induced emf. Maximum emf materializes when the magnetic field aligns perpendicularly with the coil.

Comprehending these factors empowers engineers to craft electromagnetic systems tailored to precise requirements, optimizing their performance across diverse applications.

Induced Current and Electromagnetic Force

Building upon the foundation of induced emf, we unveil how it births electric currents. The right-hand rule becomes your trusty companion for determining current direction and magnitude.

Induced Current and Electromagnetic Force: When emf arises in a conductor due to a changing magnetic field, it triggers the flow of electric current within the conductor. The right-hand rule emerges as a beacon, aiding in calculating the direction and magnitude of this induced current.

Here’s the rule: If you point your thumb in the direction of the magnetic field (B), and let your fingers denote the conductor’s motion or the induced emf (V), your palm reveals the path of the induced current (I). This rule proves invaluable in predicting induced current behavior in diverse scenarios.

By wielding the right-hand rule, you gain the ability to decipher the direction of induced currents—an indispensable skill for dissecting and designing electromagnetic systems.

Self-Inductance and Inductors

Electromagnetic induction doesn’t merely bow to external forces. We introduce the concept of self-inductance and embark on a journey into the realm of inductors. They are the unsung heroes of electrical circuits, armed with practical applications and significance.

Self-Inductance and Inductors: Beyond the influence of external magnetic fields, conductors possess self-inductance. Self-inductance, symbolized as L, quantifies a conductor or a coil of wire’s capability to induce emf in itself when its current undergoes change.

Enter inductors, the purposeful components designed to harness self-inductance. Typically, they take the form of wire coils that stockpile energy within their magnetic fields as current flows through them. When this current fluctuates, the stored energy is released, ushering in emf within the coil. Inductors are veritable Swiss Army knives in electrical circuits, filtering high-frequency noise, storing energy, and timing elements in oscillators.

Familiarity with self-inductance and inductors is paramount in crafting circuits for a plethora of applications, from power supplies to radios and telecommunications devices.

Mutual Inductance and Transformers

The magic of mutual inductance takes center stage as we explore its role in transformers, the unsung heroes of electrical power distribution. Witness the metamorphosis of voltage levels.

Mutual Inductance and Transformers: Mutual inductance, an enchanting phenomenon, occurs when one coil’s magnetic field induces emf in another nearby coil. The degree of mutual inductance hinges on factors such as the number of turns in each coil, their relative positions, and the magnetic properties of the material betwixt them.

Transformers, practical devices par excellence, leverage mutual inductance to ferry electrical energy from one coil (the primary coil) to another (the secondary coil), each sporting a different number of turns. Transformers are the unsung heroes of electrical power distribution, orchestrating the transformation of voltage to levels suitable for transmission and dispersion over vast distances.

Transformers

find themselves at home in power substations, electrical appliances, and electronic gadgets—indispensable to the tapestry of modern electrical systems.

Applications of Electromagnetic Induction

This segment breathes life into electromagnetic induction through real-world applications. Generators, alternators, induction cooktops, and magnetic card readers await your scrutiny.

Applications of Electromagnetic Induction: Electromagnetic induction manifests itself in a smorgasbord of practical applications in our daily lives and industries:

• Generators: These marvels of engineering convert mechanical energy into electrical power through electromagnetic induction. Power plants rely on generators to create electricity from diverse sources—be it fossil fuels, nuclear energy, or the breezy embrace of wind and the ceaseless flow of water.
• Alternators: Close kin to generators, alternators inhabit vehicles to recharge batteries and supply electrical vigor to vehicular systems.
• Induction Cooktops: Offering culinary precision, induction cooktops exploit electromagnetic induction to heat cookware directly and efficiently.
• Magnetic Card Readers: Devices like credit card readers and keycard systems harness electromagnetic induction to decipher information stored on magnetic stripes.

These applications underscore the practical resonance of electromagnetic induction in the tapestry of modern technology and daily conveniences.

Electromagnetic Induction in Renewable Energy

Renewable energy sources usher in a new era, and electromagnetic induction is at the forefront. Peer into the workings of wind turbines and hydroelectric generators as they tap into nature’s bounty through induction.

Electromagnetic Induction in Renewable Energy: Renewable energy sources, such as the breath of the wind and the flowing embrace of water, present sustainable alternatives to fossil fuels. Electromagnetic induction plays a pivotal role in these domains:

• Wind Turbines: These graceful giants harness the kinetic energy of the wind to rotate a generator’s rotor, summoning emf and generating electricity. The principles of electromagnetic induction breathe life into the conversion of wind energy into electrical power.
• Hydroelectric Generators: Nestled within hydroelectric power plants, these generators revel in the cascade of water. Falling water sets turbines spinning, and in turn, induces emf, birthing electricity. Electromagnetic induction dances at the core of clean, renewable hydroelectric power generation.

These renewable power sources embrace electromagnetic induction to usher in a more sustainable and ecologically aware energy future.

Experiments and Demonstrations

Learning springs to life through hands-on experiments. Detailed instructions and safety measures accompany a series of captivating experiments that let you witness electromagnetic induction firsthand.

Experiments and Demonstrations: To truly grasp electromagnetic induction, nothing surpasses practical experimentation. In this section, we unveil a series of hands-on experiments and demonstrations that grant you a front-row seat to the marvels of electromagnetic induction.

Experiment 1: “Generating Electricity with a Simple Coil and Magnet” – Here, you’ll construct a basic generator using a coil of wire and a magnet. By rotating the magnet within the coil, you’ll witness the birth of emf and the emergence of electrical current.

Experiment 2: “Lenz’s Law in Action” – This experiment exemplifies Lenz’s Law, demonstrating how a moving magnet begets a current in a coil—one that opposes the magnet’s motion.

Experiment 3: “Transforming Voltage with a Miniature Transformer” – Dive into the realm of mutual inductance with a miniature transformer. Witness voltage metamorphose as you connect different coils.

Safety reigns supreme during these experiments. Always adhere to recommended safety guidelines and equip yourself with appropriate protective gear.

Electromagnetic induction is more than just a scientific curiosity; it’s a force that has reshaped the way we generate and harness electrical energy. From its humble origins in the experiments of Faraday and Lenz to its pervasive applications in power generation, industry, and renewable energy, electromagnetic induction continues to drive our technological advancements.

This comprehensive exploration—from fundamental principles to practical applications—serves as a beacon, guiding future generations of scientists and engineers to innovate and harness the extraordinary power of electromagnetic induction for the betterment of society and the environment.

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Faraday’s Laws of Electromagnetic Induction

Faraday’s Law of Electromagnetic Induction is the basic law of electromagnetism that is used to explain the working of various equipment that includes an electric motor, electric generator, etc. Faraday’s law was given by an English scientist Michael Faraday in 1831. According to Faraday’s Law of Electromagnetic Induction, the induced current in the circuit is directly proportional to the rate of change of Magnetic Flux .

Let’s learn about Faraday’s Law of Electromagnetic Induction, its experiment, derivation, examples, and others in detail in this article.

Faraday’s Law Definition

The basic law of electromagnetic induction predicting how a magnetic field interacts with an electric circuit to produce the electromotive force (EMF) is called Faraday’s Law. And this phenomenon of producing the electromotive force in the electric circuit by the interaction of the magnetic field is called Electromagnetic Induction.

Faraday’s Laws of Electromagnetic Induction

Faraday has provided two laws that are the basis of modern electromagnetism. The laws are discussed below:

Faraday’s First Law of Electromagnetic Induction

Faraday’s second law of electromagnetic induction.

According to Faraday’s First Law of Electromagnetic Induction , “When the Magnetic Flux linked with closed-circuit changes, an EMF is induced in it which lasts only as long as the change in flux is taking place. If the circuit is closed then current also gets induced inside the circuit which is called ‘Induced current”. Changing the magnetic field changes the induced current in the circuit.

The image given below shows the deflection in the coil according to the law of Electromagnetic Induction.

Magnetic Fields Can be changed by,

Moving a bar magnet towards or away from the coil. Moving the coil into the magnetic field or outside the magnetic field. Rotating the coil relative to the magnet. Changing the area of a coil placed in the magnetic field.

According to Faraday’s Second Law of Electromagnetic Induction, “The magnitude of the induced emf is equal to the rate of change of magnetic flux linked with the coil.”

E = dⲫ/dt E = -N dⲫ/dt E = -N (ⲫ 2 -ⲫ 1 )/t where, E is Electromotive Force N is the Number of turns of the coil. ⲫ is the Flux Change

Lenz’s Law Definition

Lenz’s Law is named after the German physicist “Emil Lenz “, who formulated it in 1834. According to Lenz Law, “the direction of induced current in a circuit is such that it opposes the change in magnetic flux produced.” It is a scientific law that specifies the direction of induced current but states nothing about its magnitude. 

According to Faraday’s Second Law of Electromagnetic Induction,

E = -N(d∅/dt)

Here, the negative sign indicates that the direction of induced emf is such that it opposes the change in magnetic flux which is in accordance with Lenz’s law

Faraday’s Experiments

Faraday has performed three experiments that form the basis of electromagnetic induction.

Experiment 1

In this experiment, Faraday took a circular coil and connected it with a galvanometer and now he takes a strong bar magnet. When the north pole of the bar magnet is moved towards the coil, the galvanometer showed deflection to the right side of the zero mark in the galvanometer. When the magnet is moved away from the coil again it showed deflection but in the opposite direction. Similarly, the experiment is done with the south pole of the bar magnet, again the deflection is observed but opposite to the direction shown by the north pole of the bar magnet. When the magnet is held stationary near the coil, no deflection is observed in the galvanometer.  Conclusion: As the magnet is moved closer to the coil the magnetic flux increases hence, an induced current setup in the coil in one direction. When the magnet is moved away from the coil, the magnetic flux decreases, hence an induced current set up in the coil in the opposite direction. When the magnet is held stationary near the coil, there is no change in the magnetic flux.

Experiment 2

In this experiment, the bar magnet is kept stationary and the coil is moved. The same result is observed in experiment 1. When the relative motion between the magnet and coil is fast, the deflection in the galvanometer is larger and vice versa.

Experiment 3

As you can see from the figure below. Two coils primary (p) and secondary (s), are wound on cylindrical support. The primary coil is connected to a key, a rheostat, and a battery. The secondary is connected with a galvanometer. When the key is pressed in the primary coil the galvanometer shows deflection in one direction. When the key is released, it again shows deflection but in the opposite direction. When the key is kept pressed steady current flows through the primary coils, and the galvanometer does not show any deflection. When the current in the primary coil is increased with the help of the rheostat, the induced current flows in the secondary coil in the same direction as that of the primary coil.

The image given below shows the setup of Faraday’s Experiment.

All three Faraday Experiments can be summarised in the table given below,

Faraday Law Formula

Faraday Law formula can be easily calculated as suppose we take a bar magnet approaching a coil and we measure the flux associated with the coil at two-time instances T 1 and T 2 . The change in flux results in the production of EMF which causes electrons to move to constitute current.

The image given below tells us about the change in electromagnetic force linked with the coil when the magnet moved close to the coil.

At T 1 , the flux associated with the coil = Nϕ 1

At T 2 , the flux associated with the coil = Nϕ 2

Change in flux = N(ϕ 1 – ϕ 2 ) = Nϕ

Rate of change of flux = Nϕ/t

Taking the derivative, and equating it with E(electromotive force), according to Faraday’s law of electromagnetic induction, the rate of change of flux is equal to induced emf.

Considering Lenz’s Law the emf opposes the cause which produces it,

E = -Ndϕ/dt where, E is the electromotive force Φ is the flux measured in the coil N is the number of turns in the coil

Faraday’s Law Derivation

The derivation of Faraday’s Law is explained below:

Now we take a magnet approaching a coil and consider instances at times T 1 and T 2 At time T 1 flux linked with the coi l = NΦ 1 At time T 2 flux linked with the coil = NΦ 2 Change in flux = N(Φ 2 – Φ 1 ) Rate of change of flux = N(Φ 2 – Φ 1 ) / t Taking the derivative of the above equation, we get Derivative of Rate of Change of Flux = N dΦ/dt Faraday’s second law of electromagnetic induction, says that the induced emf in a coil is equal to the rate of change of flux associated with the coil. Thus, E = – N dΦ/dt…(1) The negative sign is added as it helps to accommodate Lenz’s law.

Change in Electromagnetic Force

Electromagnetic Force linked with the coil can easily be changed by following the steps discussed below.

Induced EMF can easily be increased by increasing the number of turns in the coil. If the magnetic field strength increases induced EMF also increases

Applications of Faraday’s Law

Faraday’s law has various applications and some of the common applications of Faraday’s Law are,

Faraday’s Law is used in electrical equipment like transformers and electric motors. Induction cooker works on the principle of mutual induction, which is derived from Faraday’s law. Faraday’s law is also helpful in designing musical instruments like the electric guitar, electric violin, and others.

How To Increase EMF Induced in a Coil

The emf of the coil can be increased by following the steps discussed below,

By Increasing the Number of Turns in the Coil. By Increasing Magnetic Field Strength. By Increasing the Speed of the Relative Motion between Coil and Magnet.

Thus, the steps discussed above increase the induced emf induced in a coil.

Parallel Plate Capacitor Gauss’s Law Coulomb’s Law

Solved Examples on Faraday’s Law of Electromagnetic Induction

Example 1: The magnetic flux linked with a coil is changed from 2Wb to 0.2Wb in 0.5 seconds. Calculate the induced emf.

Δⲫ = 0.2-2 = 1.8wb Δt = 0.5 sec E = -(Δⲫ/Δt) E= -1.8/0.5 volts E= -3.6 volts Therefore, induced emf will be -3.6 volts.

Example 2: In a coil of resistance 200, a current is induced by changing the magnetic flux through it as shown in the figure. Calculate the magnitude of change in flux through the coil.

dq = – (N/R) dt i = (1/R). (dq/dt) Δⲫ = R.Δq Δⲫ = 200 × (Area of circular graph) Δⲫ = 200 × (1/2×20×0.5) Δⲫ = 200 × 5 Δⲫ = 1000 Wb Therefore, magnitude of change in flux is 1000 Wb.

Example 3: Calculate the emf induced in the wire. When a small piece of metal wire dragged across the gap between the pole pieces of a magnet in 0.6sec. The magnetic flux between the pole pieces is known to be 9×10 -4 Wb.

dt = 0.5 s dⲫ = 9×10 -4 -0 = 9×10 -4 Wb E = (dⲫ)/dt E= (9×10 -4 )/0.6 E= 0.0036 V Therefore, the induced emf 0.0036V

FAQs on Faraday’s Law of Electromagnetic Induction

Q1: what is faraday’s law of electromagnetic induction.

There are two laws explained by Faraday called Faraday’s Laws of Electromagnetic Induction. First law explains the induction of emf in a conductor and the second law tells the emf produced in the conductor. 

Q2: What is Faraday’s First Law of Electromagnetic Induction?

Faraday’s first law of Electromagnetic Induction states that, “ An EMF is produced when a conductor is placed in a varying magnetic field”, and the current produced in this process is called Induced Current.

Q3: What is Faraday’s Second Law of Electromagnetic Induction?

Faraday’s second law of Electromagnetic Induction states that, “ The rate of change of flux is directly proportional to the induced current in a coil.”

Q4: Why are Faraday’s Laws important?

Faraday’s law is used to define the EMF produce inside a coil if it rotates in a magnetic field. This concept is widely used in modern-day physics. It is used in electric motors. It is used in electric generators.

Q5: What is meant by EMF?

EMF also called Electromotive Force is the energy required to flow the current in the circuit.

Q6: What is Faraday’s Formula?

The Faraday law formula is, E = -Ndϕ/dt where, E is the electromotive force Φ is the flux measured in the coil N is the number of turns in the coil

Q7: What are the Applications of Faraday’s law?

Various applications of the Faraday laws are, It used to explain the working Electric Transformer and Electric Motor It explains the forces acting on the electric circuit by the electromagnetic field.

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