Question

A circular copper disc 10 cm in diameter rotates at 1800 revolution per minute about an axis through its centre and at right angles to disc. A uniform field of induction B of 1 Wb m-2 is perpendicular to disc. What potential difference is developed between the axis of the disc and the rim?

• A. 0.023 V
• B. 0.23 V
• C. 23 V
• D. 230 V

Answer 1

Answer: (B)

0.23 V

Answer 2

Here $l = r = 5cm = 5 \times 10^{- 2}m$

$\omega = 2\pi\left( \frac{1800}{60} \right)rads^{- 1} = 60\pi rads^{- 1}$

$B = 1Wbm^{- 2}$

$\varepsilon = \frac{1}{2}Bl^{2}\omega = \frac{1}{2} \times 1 \times (5 \times 10^{- 2})^{2} \times 60\pi = 0.23V$