CBSE Class 10 Science 2022 · Paper 31/4/2 · Question 14

(a) A galvanometer detects the presence of a current in a circuit and shows its direction, its pointer deflecting to the left or right of the centre zero; the induced current is usually small and brief, so this sensitive detector is used. While the magnet moves towards the coil, the magnetic field linked with the coil changes, which induces a potential difference and a current in the coil, so the needle deflects. When the motion stops, the field stops changing, the induced current stops and the needle returns to zero, so the deflection is momentary. (b) Because there is still relative motion between the coil and the magnet: as the coil moves towards the south pole, the magnetic field linked with the coil changes, so a current is induced in it and the galvanometer deflects. It does not matter whether the magnet or the coil moves. (c)(i) Conclusion: relative motion between a magnet and a coil, which changes the magnetic field linked with the coil, induces a potential difference and an electric current in the coil (electromagnetic induction); the current flows only while the field is changing. Yes, the momentary deflection increases: more turns and a stronger magnet both increase the induced potential difference, and so the induced current, for the same motion. OR (c)(ii) Electromagnetic induction is the production of a potential difference, and hence a current, in a conductor such as a coil when the magnetic field linked with it changes. When a strong bar magnet is held stationary near one end of the coil, the galvanometer shows no deflection: the field through the coil is not changing, so no current is induced, however strong the magnet.