question_answer 69)

  Explain the phenomenon of electromagnetic induction. Describe an experiment to show that a current is set up in a closed loop when an external magnetic field passing through the loop increases or decreases.

Answer:

                  This phenomenon was discovered by Michael Faraday and Joseph Henry in 1831. The phenomenon of generation of an electric current in a closed circuit from magnetic effects1.e., by changing the magnetic field is called electromagnetic induction. Electric current produced due to this phenomenon is called induced current. The potential difference set in the circuit due to induced current is called induced emf. Experiment Let two different coils of copper wire, namely coil 1 and coil 2, having large number of turns are arranged as per the circuit diagram as shown in figure. The coil 1, having larger number of turns, is connected in series with a battery and a plug key whereas the other coil 2 is connected with a galvanometer as shown in circuit diagram. When key K is closed, the galvanometer shows a deflection in its needle instantly jumps to one side and just as quickly returns to zero, indicating a momentary current in coil 2. This happens due to an external magnetic field passing through the loop increases. When key K is open, the coil 1 is disconnected from the battery. The needle momentarily moves ,but to the opposite side. It means that now the current flows in the opposite direction in coil2. This happens due to an external magnetic field passing through the loop decreases.