1 Experiments of Faraday and Henry Magnetic Flux _ Faraday_s Law of Induction

Experiments of Faraday and Henry Magnetic Flux & Faraday’s Law of Induction

Faraday’s Experiments

Experiment 1 − Current induced by a magnet

The relative motion between the magnet and the coil generates electric current in the coil. The current so generated is called induced current.

Experiment 2 − Current induced by a current

When the bar magnet is replaced by a second coil C2 connected to a battery, the steady current in coil C2 produces a steady magnetic field. As coil C2 is moved towards coil C1, the galvanometer shows a deflection. This indicates that electric current is induced in coil C1. When C2 is moved away, the galvanometer shows a deflection again, but this time in the opposite direction. The deflection lasts as long as coil C2 is in motion.

Experiment 3 − Current induced by changing current

The figure shows two coils C1 and C2 held stationary. Coil C1 is connected to galvanometer G while the second coil C2 is connected to a battery through a tapping key k.
It is observed that the galvanometer shows a momentary deflection when the tapping key k is pressed. If the key is held pressed continuously, there is no deflection in the galvanometer. When the key is released, a momentary deflection is observed again, but in the opposite direction.

Magnetic Flux

The magnetic flux Φ through any surface held in a magnetic field is measured by the total number of magnetic lines of force crossing the surface.

Where, θ is the smaller angle between and , which normal to the surface area makes with

• Units of magnetic flux − The SI unit of magnetic flux is Weber (Wb). One Weber is the amount of magnetic flux over an area of 1 m2 held normal to a uniform magnetic field of one tesla.
1 Weber = 1 tesla × 1 m2
The c.g.s unit of Φ is Maxwell (Mx).
1 Weber = 108 Maxwell

Faraday’s Law of Electromagnetic Induction
First law − Whenever the amount of magnetic flux linked with a circuit changes, an emf is induced in the circuit. The induced emf lasts as long as the change in magnetic flux continues.
Second law − The magnitude of emf induced in a circuit is directly proportional to the rate of change of magnetic flux linked with the circuit.
According to Faraday’s second law, induced emf