Faraday Electromagnetic Induction Experiment

What is the Electromagnetic Induction Experiment?

Electromagnetic induction is the mechanism by which a current can be caused to flow due to a magnetic field transition.

Michael Faraday Experiment

  • Faraday first discovered in 1831 that whenever the number of magnetic lines of forces in the circuit changes, the emf is produced in the circuit and is known as induced emf, a phenomenon known as electromagnetic induction.

  • If the circuit is closed, the current flows through it, which is known as the induced current.

  • This induced emf and current lasts only for a time while the magnetic flux changes.

  • Two examples of the kind that Faraday and Henry have done

(i) Experiment - 1

  • The following figure shows a closed circuit containing an insulated wire coil. 

  • Also note that the circuit contains no source of emf, so there is no deflection in the galvanometer.

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  • If we move the bar magnet towards the coil keeping the coil stationary with the north pole of the magnet facing the coil (say) then we notice a deflection in the needle of the galvanometer indicating the pressure of the current in the circuit.

  • This deflection is observed only for the interval of time during which the magnet is in motion. Now, if we start pushing the magnet in the opposite direction, the galvanometer needle is now deflected in the opposite direction.

  • Again, if we move the magnet towards the coil, with its south pole facing the coil, the deflection is now in the opposite direction, again indicating that the current now set in the coil is in the opposite direction to that when the north pole faces the wire. 

  • Deflection is also observed in the galvanometer when the magnet is stationary and the circuit is moved away from the magnet.

  • It is also found that the motion of the magnet is higher, the deflection in the galvanometer needle is greater. 

  • From this experiment, Faraday assumed that the magnet moving in one direction towards the coil had the same effect pushing the coil in the other direction towards the magnet.

(ii) Experiment - 2

  • Figure - 2 below shows the primary coil P connected to the battery and the secondary coil connected to the galvanometer.

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  • Now we have replaced the magnet from the previous experiment with a current-carrying coil and expect to experience a similar effect as the current-carrying coil generates a magnetic field. 

  • The motion of either of the coils shows the deflection of the galvanometer.

  • The galvanometer also shows a sudden deflection in one direction when the current started in the primary coil and in the opposite direction when the current stopped.

Magnetic Flux:

It is the number of magnetic field lines that cross any surface that is usually referred to as magnetic flux (ϕ) across that surface.

ϕ = B.A cos θ

Where B is a magnetic field, A is a surface field, ϕ  is the angle between the magnetic field and the area vector. SI unit of magnetic flux is weber.

Electromagnetic Induction Experiment Explanation

Electromagnetic Induction:

It is a phenomenon of e.m.f. production in a conductor due to a change in the magnetic flux associated with it. The e.m.f thus produced is called induced e.m.f. and the current is called the induced current.

Faraday’s Law of Electromagnetic Induction:

The magnitude of the induced emf in the circuit is equal to the time rate of change of the magnetic flux in the circuit. Mathematically, the induced emf is given by ε = ‒ (dϕ/dt).

The negative sign indicates that the current caused in a circuit often flows in such a direction that it opposes the change or causes that it opposes the change or causes the change.

In the case of a tightly wound N-turn coil, the change in the flux associated with each turn is the same. The expression for the total induced emf is therefore given by -

ε = ‒ N (dϕ/dt).

The induced emf can be improved by increasing the number of N turns of the closed coil.

Flows may be changed by altering one or more of the words B, A and θ.

FAQ (Frequently Asked Questions)

Q1. Explain Faraday's Law

Michael Faraday was an English scientist of the 19th century, credited with many great discoveries in the field of physics and chemistry, specifically on the relationship between current and magnets, and electrochemistry. Law of Faraday, by the 19th-century physicist Michael Faraday. This relates the rate of magnetic flux shift through the loop to the magnitude of the electromotive force E caused by the loop. There's a relationship which is stated as - 

E =  dΦ​ / dtE

The electromotive force or EMF refers to the potential difference between the unloaded loop (i.e. when the resistance in the circuit is high). In practice, it is always necessary to regard EMF as a voltage, because both the voltage and the EMF are calculated using the same unit, the volt.

Q2. A Small 10 mm Diameter Permanent Magnet Produces a Field of 100 mT. The Field Drops Away Rapidly with Distance and is Negligible More than 1 mm from the Surface. If this Magnet Moves at a Speed of 1 m/s through a 100-turn Coil of Length 1 mm and Diameter just Larger than the Magnet, what is the EMF Induced?

We can use Faraday 's induction law to find the induced EMF. This needs us to know the change in the flow through the coil and how quickly the change is going to happen.

We can start by looking at the cases where the magnet is outside and inside the coil separately. Since we are told that the field decays quickly, we can assume that the flux is zero when the magnet is outside the coil. Since the coil is a close fit around the magnet, we can assume that the field is always orthogonal to the coil and that the flux is orthogonal.

 Φ=BA

Since the magnet is considered to be traveling at 1000 mm / s, we know that it will be inside a 1 mm long coil for just 1/1000 s (1 ms). So by applying Faraday 's law,

E = -N dΦ / dt 

= - (100 turns) (100. 10-3 T) (5. 10-3 m )2 / 1. 10-3 s

= o.78 V