Physics MCQs for NEET — Practice Questions with Answers

As the loop moves out of the field, the magnetic flux decreases. According to Lenz's law, the induced current will flow in a direction that creates a magnetic field to oppose this decrease, meaning it will try to 'pull' the loop back into the field, or effectively, try to keep the flux from decreasing. (Refer to NCERT Example 6.4 (ii & iii), where outward motion causes a decrease in flux, and induced current flows to oppose this decrease.)

According to the NCERT text, 'The energy required to build up the current I is, $W = \frac{1}{2}LI^2$ (6.17)'. This formula is derived from the work done against the back emf to establish the current in the inductor.

The NCERT text states, 'work needs to be done against the back emf (ε) in establishing the current. This work done is stored as magnetic potential energy.'

The NCERT text mentions, 'This expression reminds us of $mv^2/2$ for the (mechanical) kinetic energy of a particle of mass m, and shows that L is analogous to m (i.e., L is electrical inertia and opposes growth and decay of current in the circuit).'

Example 6.9 (b) in the NCERT text derives the magnetic energy per unit volume as, '$u_B = \frac{B^2}{2\mu_0}$ (6.18)'.

The NCERT text states, 'We have already obtained the relation for the electrostatic energy stored per unit volume in a parallel plate capacitor (refer to Chapter 2, Eq. 2.73), $u_E = \frac{1}{2} \epsilon_0 E^2$ (2.73). In both the cases energy is proportional to the square of the field strength.'

The energy stored in an inductor is given by $W = \frac{1}{2}LI^2$. If the current I is doubled to 2I, the new energy $W' = \frac{1}{2}L(2I)^2 = \frac{1}{2}L(4I^2) = 4 (\frac{1}{2}LI^2) = 4W$. Thus, the energy becomes four times.

The NCERT text mentions, 'The SI unit of inductance is henry and is denoted by H. It is named in honour of Joseph Henry who discovered electromagnetic induction in USA, independently of Faraday in England.'

According to the NCERT text, 'Inductance... has the dimensions of [M L$^2$ T$^{-2}$ A$^{-2}$] given by the dimensions of flux divided by the dimensions of current.'

The NCERT text states, 'For the current I at an instant in a circuit, the rate of work done is $\frac{dW}{dt} = I\epsilon$.'