Question

Suppose the resistance of the coil in the previous problem is 25Ω. Assume that the coil moves with uniform velocity during its removal and restoration. Find the thermal energy developed in the coil during (a) its removal, (b) its restoration and (c) its motion.

Answer 1

Given:
Resistance of the coil, R = 25 Ω

(a) During the removal the emf induced in the coil,
e = 50 V
time taken, t = 0.25 s
current in the coil, $i=\frac{e}{\mathrm{R}}=2\mathrm{A}$
Thus, the thermal energy developed is given by
H = I²RT
= 4 × 25 × 0.25 = 25 J
(b) During the restoration of the coil,
emf induced in it, e = 50 V
time taken, t = 0.25 s
current in the coil, $i=\frac{e}{\mathrm{R}}=2\mathrm{A}$
Thus, the thermal energy developed is given by
H = i²RT = 25 J

(c) We know that energy is a scalar quantity. Also, the net thermal energy is the algebraic sum of the two energies calculated.
∴ Net thermal energy developed
= 25 J + 25 J = 50 J