Question

When 100 volt dc is applied across a coil, a current of 1 amp flows through it. When 100 volt ac at 50 cycle$s^{- 1}$ is applied to the same coil, only 0.5 ampere current flows. The impedance of the coil is

• A. $100\Omega$
• B. $200\Omega$
• C. $300\Omega$
• D. $400\Omega$

Answer 1

Answer: (B)

$200\Omega$

Answer 2

When dc is supplied

$R = \frac{V}{i} = \frac{100}{1} = 100\Omega$

When ac is supplied

$Z = \frac{V}{i} = \frac{100}{0.5} = 200\Omega$