Faraday’s Experiment
Faraday’s Experiment :- Electricity and magnetism are closely related branches of physics. In 1831, the English scientist Michael Faraday demonstrated that an electric current can be produced in a coil when there is relative motion between the coil and a magnet. This simple experiment laid the foundation of electromagnetic induction.
Electromagnetic induction is the process of generating an electromotive force (emf) or electric current in a closed circuit due to a changing magnetic flux linked with the circuit. In simple terms, whenever the magnetic field around a conductor changes, an emf is induced in the conductor, which may cause a current to flow if the circuit is closed.
Some of Faraday’s experiments are as follows :
Experiment 1
Below figure shows a coil A connected to a galvanometer G.
- Pushing the North pole of a bar magnet towards the coil makes the galvanometer needle deflect → current is induced.
- No deflection occurs if the magnet is stationary.
- Pulling the magnet away causes deflection in the opposite direction → current reverses.
- Using the South pole gives opposite deflections compared to the North pole.
- Faster motion of the magnet gives larger deflection (stronger current).
- Moving the coil instead of the magnet produces the same results.
👉 Thus, it is the relative motion between the magnet and the coil that is responsible for generation (induction) of electric current in the coil.
Experiment 2
Now a second coil B, connected to a battery, is used in place of the bar magnet. The steady current in B creates a steady magnetic field.
- Moving B towards A → galvanometer in A deflects (induced current).
- Moving B away → deflection in opposite direction.
- Deflection lasts only during motion.
- If B is fixed and A is moved, the same effects occur.
👉 Thus, relative motion between the two coils induces current in coil A.
Experiment 3
The first two experiments used relative motion (magnet–coil, coil–coil). Faraday showed motion is not always needed. Below figure shows two stationary coils, A is connected to a galvanometer G and B with a battery and key K.
- Pressing key → momentary deflection, then pointer returns to zero.
- Holding key pressed → no deflection.
- Releasing key → momentary deflection in opposite direction.
- Deflection increases greatly if an iron rod is placed inside the coils.
👉 Thus, current is induced by changing magnetic field, even without physical motion.
Conclusion of Faraday’s Experiment :
From Faraday’s experiments we learn that an electric current can be induced in a coil :
- By moving a magnet towards or away from a coil (relative motion of magnet and coil).
- By moving one current-carrying coil towards or away from another coil (relative motion of two coils).
- Even without motion, by changing the magnetic field in a coil (e.g., pressing or releasing a key in a nearby current-carrying coil).
👉 Hence, the fundamental cause of induced current is a changing magnetic field.