Question

A bar of length 0.15 m slides along metal rails at a speed of 5 m/s. The bar and rails are in a magnetic field of 40 T, pointing out into the page. The resistance of two resistors in parallel is both 20 Ω, and the resistance of the bar is 5 Ω. What is the current in the bar?

(a) 1 A

(b) 2 A

(c) 3 A

(d) 5 A

I have been asked this question during an online exam.

My doubt is from Electromagnetic Induction in section Electromagnetic Induction of Physics – Class 12

Answer 1

The correct choice is (b) 2 A

Explanation: L = 0.15 m; B = 40 T; v = 5 m/s; R1 = 10 Ω; R2 = 10 Ω; R3 = 5 Ω

Emf (E) = vLB = 5 × 0.15 × 40

E = 5 × 6

E = 30 V

R1 and R2 are in parallel ➔ \(\frac {1}{R} = \frac {1}{R1} + \frac {1}{R2} = \frac {1}{20} + \frac {1}{20} = \frac {2}{20} = \frac {1}{10}\) ➔ R = 10 Ω

RTOT = R + R3 = 10 + 5 = 15 Ω

Therefore, current (I) = \(\frac {E}{R}\)

I = \(\frac {30}{15}\)

I = 2 A