Question

One section AB of a circuit absorbs 53.0 W of power when a current i = 1.20 A passes through it in the direction shown.
(a) Find the potential difference between A and B.
(b) If element C does not have an internal resistance, what is its emf?
(c) Which terminal left or right is positive?

Answer 1

Let ‘r’ be the internal resistance of C. The power relation is
i²(R + r) = 53.0 But R = 19.0 and i = 1.20 A
r = \(\frac{53.0}{(1.2)^{2}}\) – 19.0 = 17.8 Ω

(a) p.d between A and B is i(R + r) = 1.2 (19 + 17.8) = 44.2 V

(b) In the absence of r, i²R + i ε = 53
ε = \(\frac{53-\mathrm{i}^{2} \mathrm{R}}{\mathrm{i}}\)

(c) Since the current is directed from left to right, terminal A is positive.