The magnetic field energy in an inductor changes from maximum value to minimum value in 5 ms, when connected to an a.c. source. The frequency of the source is

Question

The magnetic field energy in an inductor changes from maximum value to minimum value in 5 ms, when connected to an a.c. source. The frequency of the source is (A) 50 Hz (B) 20 Hz (C) 200 Hz (D) 500 Hz

Tardigrade Admin · Accepted Answer

Magnetic field energy of a coil is given by

\frac{1}{2} L I^{2}

In this case I changes from maximum to zero value in 5 ms

i . e .

in T/4 ms

∴

T/4 = 5 ms or T = 5

\times

4 = 20 ms =

20 \times 1 0^{- 3}

s
Then, frequency

ν = \frac{1}{T} = \frac{1}{20 \times 1 0 ^{- 3}}

= 50 Hz

Q. The magnetic field energy in an inductor changes from maximum value to minimum value in 5 ms, when connected to an a.c. source. The frequency of the source is

50 Hz

20 Hz

200 Hz

500 Hz

Magnetic field energy of a coil is given by 21​LI2 In this case I changes from maximum to zero value in 5 ms i.e. in T/4 ms ∴ T/4 = 5 ms or T = 5 × 4 = 20 ms = 20×10−3 s Then, frequency ν=T1​=20×10−31​ = 50 Hz

Magnetic field energy of a coil is given by $\frac{1}{2} L I^{2}$ In this case I changes from maximum to zero value in 5 ms $i . e .$ in T/4 ms $∴$ T/4 = 5 ms or T = 5 $\times$ 4 = 20 ms = $20 \times 1 0^{- 3}$ s
Then, frequency $ν = \frac{1}{T} = \frac{1}{20 \times 1 0 ^{- 3}}$ = 50 Hz