Electromagnetic Induction MCQs for NEET — Physics Questions with Answers

The NCERT text defines $\varepsilon_0$ as, 'where $NBA \omega$ is the maximum value of the emf... If we denote $NBA \omega$ as $\varepsilon_0$, then $\varepsilon = \varepsilon_0 \sin \omega t$ (6.20)'.

The text states, 'Note from Fig. 6.14 that the emf has its extremum value when $\theta = 90^{\circ}$ or $\theta = 270^{\circ}$, as the change of flux is greatest at these points.'

The NCERT text mentions, 'The ends of the coil are connected to an external circuit by means of slip rings and brushes.'

The NCERT text explains, 'Since $\omega = 2\pi n$, Eq (6.20) can be written as $\varepsilon = \varepsilon_0 \sin 2\pi n t$ (6.21) where $n$ is the frequency of revolution of the generator’s coil'.

The NCERT text states, 'Since the value of the sine function varies between +1 and –1, the sign, or polarity of the emf changes with time.'

The NCERT text explicitly states, 'The Yugoslav inventor Nicola Tesla is credited with the development of the machine (AC generator).'

The NCERT text states, 'In commercial generators, the mechanical energy required for rotation of the armature is provided by water falling from a height, for example, from dams. These are called hydro-electric generators.'

Lenz's law is a consequence of the law of conservation of energy. The induced current's direction is such that it opposes the change in magnetic flux, thus requiring external work to maintain the change, which is then dissipated as heat. If it aided the change, it would generate energy spontaneously, violating conservation of energy. (Refer to NCERT text: 'This violates the law of conservation of energy and hence can not happen.')

As the North pole approaches, the magnetic flux increases. To oppose this increase, the induced current creates a magnetic field with its North pole facing the approaching magnet, resulting in a repulsive force. By the right-hand thumb rule, this corresponds to a counter-clockwise current as observed from the side of the magnet. (Refer to NCERT text: 'As the North-pole of the bar magnet moves towards the coil, the magnetic flux through the coil increases. Hence current is induced in the coil in such a direction that it opposes the increase in flux. This is possible only if the current in the coil is in a counter-clockwise direction with respect to an observer situated on the side of the magnet.')

When the North pole of the magnet is withdrawn, the magnetic flux through the coil decreases. To oppose this decrease, the induced current creates a magnetic field with a South pole facing the receding North pole of the magnet, resulting in an attractive force that tries to prevent the magnet from being withdrawn. (Refer to NCERT text: 'Similarly, if the North-pole of the magnet is being withdrawn from the coil, the magnetic flux through the coil will decrease. To counter this decrease in magnetic flux, the induced current in the coil flows in clockwise direction and its South-pole faces the receding North-pole of the bar magnet. This would result in an attractive force which opposes the motion of the magnet and the corresponding decrease in flux.')