Question

At t = 0, the current through a 65.0 mH inductor is 42.5 mA and is increasing at the rate of 62.5 mA/s .

Part A

What is the initial energy stored in the inductor, and how long does it take for the energy to increase by a factor of 6.5 from the initial value?

Express your answer using three significant figures.

U =?

Part B

Express your answer using two significant figures.

t = ?

Answer 1

According to the given problem,

A) The initial energy stored in the inductor,

U = 1/2LI²

= 0.5*65.0*10^-3*(42.5*10^-3)²

= 5.87*10^-5J

B) Now the energy becomes a factor of 6.5,

U' = 6.5*U = 3.82*10^-4 J

Now using this calcualt the current in the inductor,

I = ?2U'/L

= 0.1085 A = 108.35mA

Given the chage in current,

62.5mA/s = 108.35mA - 42.5mA/t

t = 65.85/62.5

t = 1.054s.

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