Our Objective

To demonstrate the production of induced emf in a coil due to the movement of (i) a magnet towards and away from it (ii) similar coil carrying current towards and away from it.

 

The Theory

Michael Faraday discovered law of electromagnetic induction 

Law of electromagnetic induction

The magnitude of the induced emf in a circuit is equal to the time rate of change of magnetic flux through the circuit. 

ε = - d Φ/dt 

ε - Induced emf  

Φ - Magnetic flux 

Φ = BA cosθ 

B - Magnetic field 

A - Area of the surface 

θ - Angle between the magnetic field and surface 

Magnetic flux can change by varying Magnetic field, Area of the surface, angle between the magnetic field and surface 

The negative sign indicates the direction of e and hence the direction of current in a closed loop 

Michael Faraday conducted different experiments to reach electromagnetic induction. 

Production of induced emf in a coil due to the movement of a magnet towards and away from it

Fig: When the bar magnet is pushed towards the coil, the pointer in the galvanometer G deflects.

Connect coil with galvanometer.  Move magnet towards coil. Pointer in the galvanometer deflects. It indicates the presence of the current. The pointer in the galvanometer deflects in the opposite direction when the magnet moves away from the coil. Deflection in galvanometer happens when magnet moves towards the coil or away from the coil. You can see the deflection of pointer in galvanometer in the opposite direction if you move opposite face of the magnet towards coil. Direction of deflection of the pointer in the galvanometer will be different when we bring north pole of the magnet towards the coil and when we bring south pole of the magnet towards the coil. Deflection of the pointer in galvanometer happens when we move the coil or magnet 

Relative motion between magnet and coil induces electric current on coil with galvanometer. Deflection of pointer in galvanometer increases as the speed of the magnet increases. 

When we bring magnet towards the coil magnetic field through coil increases. It causes emf in coil. Current induces in the coil. When we bring magnet away from the coil magnetic field through coil decreases. It causes emf in coil. Current induces in the coil. Direction of the current will be different from previous case. 

Production of induced emf in a coil due to the movement of similar coil carrying current towards and away from it.

Case 1 

Replace the magnet with coil C₂ which is connected to battery. The pointer in the galvanometer deflects when coil C₂   brings towards or away from coil C₁ with galvanometer. Deflection of the pointer in galvanometer happens when we move the coil C₁ or coil C₂. 

Relative motion between coils induces electric current on coil with galvanometer.

Fig: Current is induced in coil C1 due to motion of the current carrying coil C2.

When we bring coil C₂ towards the coil magnetic field through coil C₁ increases. It causes emf in coil C₁. Current induces in the coil C₁. When we bring coil C₂ away from the coil magnetic field through coil C₁ decreases. It causes emf in coil. Current induces in the coil. Direction of the current will be different from previous case. 

Case- 2 

Fig: Experimental set-up.

In this experiment coil C₂ is connected to battery through key. The pointer in the galvanometer deflects when we close the key and open the key. The direction of deflection of the pointer in the galvanometer will be different when we close the key or open the key. 

When we close the key current increases from 0 to maximum value. Current through the coil C₂ 

Increases. Magnetic field through coil C₂ increases. It causes emf in coil C₁. Current induces in the coil C₁. When we open the key current decreases from maximum to 0 value. Current through the coil C₂  

decreases. Magnetic field through coil C₂ decreases. It causes emf in coil C₁. Current induces in the coil C₁. Direction of the current will be different from previous case. 

Case-3 

You can repeat the experiment by connecting the coil C₂ through rheostat. Vary the current by moving slider of rheostat. The pointer in the galvanometer deflects when we vary current through coil C₂. The direction of deflection of the pointer in the galvanometer will be different when we increase and decrease current. 

When current through coil C₂ changes magnetic field through the coil C₁ changes. It causes emf in coil C₁.

Case-4 

You can repeat the experiment by changing the common area between the coils C₁ and C₂. The pointer in the galvanometer deflects when we change the common area between the coils C₁ and C₂. The direction of deflection of the pointer in the galvanometer will be different when we increase and decrease the common area between the coils. 

When we change the common area between the coil changes magnetic flux through the coil C₁ changes. It causes emf in the coil C₁. It causes the current in coil C₁.

Direction of induced emf can be found using Lenz’s law- 

Lenz's law states that “the polarity of induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produced it.” 

 

Learning Outcomes

• Students understand about the Faraday’s law.
• Students understand which factors depend upon the induced emf.