Question

An electric lamp is marked 100 W, 220 V. If it operates at 200 V, the current through it will be:

• A. 2.2 A
• B. 2 A
• C. 0.5 A
• D. none of the above.

Answer 1

Answer: (D)

none of the above.

Answer 2

$P = \frac{V^2}{R}$ . Hence $R= \frac{V^2}{P} = [ \frac{(220)^2}{100} ] = 484 \, \Omega$ When potential is 200 V, the current will be given by $\frac{V}{R} = \left( \frac{200}{484}\right)$ A = 0.41 A.