Question

How would the current in coil be altered if (a) the coil has twice as many turns, (b) the coil was to move three times as fast ?

• A. (a) current becomes twice (b) current remains same.
• B. (a) current remains same (b) current becomes thrice.
• C. (a) current becomes half (b) current becomes one third.
• D. (a) current becomes twice (b) current becomes thrice.

Answer 1

The correct option is D (a) current becomes twice (b) current becomes thrice.

Case (a) current becomes twice:
When a current carrying coil is moved closer to the magnet it will generate electricity as the coil moves through the magnetic field. As the current carrying coil is moved, there will be an induced electro-motive force (EMF) which can cause a current in the coil. Once the coil stops moving, the current will go to zero. Hence, when a galvanometer is connected to the circuit, there will be deflection due to the flow of electricity. As the coil is moved towards the magnet, the needle of the galvanometer moves one direction. As the coil is moved away from the magnet, the needle of the galvanometer moves the opposite direction. If the coil is moved faster, the magnitude of the deflection increases. Also, in a condition when the number of turns in the coil is doubled the current through the coil is also doubled because the amount of current flowing through the coil is directly proportional the number of turns in the coil.
Case (b) current becomes thrice:
When a current carrying coil is moved closer to the magnet it will generate electricity as the coil moves through the magnetic field. As the coil is moved, there will be an induced electro-motive force (EMF) which can cause a current in the coil. Once the coil stops moving, the current will go to zero. Hence, when a galvanometer is connected to the circuit, there will be deflection due to the flow of electricity. As the coil is moved towards the magnet, the needle of the galvanometer moves one direction. As the coil is moved away from the magnet, the needle of the galvanometer moves the opposite direction. If the coil is moved faster, the magnitude of the deflection increases. Thus, the current is increased three times when the magnet is moved three faster towards the coil because the magnitude of deflection is directly proportional to speed of magnet's motion.