# Inductors physics forums

1. Dec 4, 2013

### dwn

1. The problem statement, all variables and given/known data

A coil with an inductance of 2.0 H and a resistance of 10 ohm is suddenly connected to an ideal battery with E = 100 V. At 0.10 s after the connection is made, what is the rate at which:

(a) energy is being stored in the magnetic field, ans: 2.4*102
(b) thermal energy is appearing in the resistance, and ans: 1.5*102
(c) energy is being delivered by the battery? ans: 3.9*102

2. Relevant equations

UL=.5LI2
VR=E(1-e-t/tau)

3. The attempt at a solution

V=IR 100/10 = I = 10 A
UL= .5*2*102 = 100

Clearly I'm missing a step or another equation to derive the current because I don't believe 10 A is correct. Please advise!

2. Dec 4, 2013

### ehild

10 A is the current after infinite time, and it is equal to Io= E/R. (E is the emf of the battery)

The current changes according to the function I=Io(1-e-t/τ).

You need to calculate the rate of changes of energies at t= 10 s.

ehild