Question

A solenoid has an inductance of 10 henry and resistance of 2 ohm l. It is connected to a 10 volt battery . How long it will take f0r the magnetic energy to reach 1/4 of its maximum value

Answer 1

Given :

Let Io be the maximum current

I be the current when the energy is 1/4th of maximum value

1/2 L I²=1/4( 1/2 L Io²)

I=Io/2

As we know that

I=Io(I-e⁻Rt/L)

e⁻Rt/L=1- I/Io

=1/2

R=2ohm

L=10 henry

e⁻rt/L=0.5

apply log

-Rt/L=log(0.5)

Rt/L=0.693

t=0.693 x 10/2 =6.93/2=3.465 sec

∴ It takes 3.465 sec for the magnetic energy to reach 1/4 of its maximum value

Answer 2

Answer:

Explanation:See this pic below for answer