Question

The magnetic field energy in an inductor changes from maximum value to minimum value in 10 ms, when connected to an a.c. source. The frequency of the source is ______.

Options

• 25 Hz

• 50 Hz  

• 200 Hz

• 500 Hz

Answer 1

The magnetic field energy in an inductor changes from maximum value to minimum value in 10 ms, when connected to an a.c. source. The frequency of the source is 25 Hz.

Explanation:

Magnetic field energy `(1/2 "LI"^2)` changes from max. to zero, when current changes from I₀ to zero i.e. in T/4 sec.

`therefore "T"/4` = 10 ms T = 40 ms =` 40 xx 1^-3` s

f = `"1"/"T" = 1/ (40xx 10^-3) = 10^3 /40` = 25 Hz