Calculating Voltage in an Electromagnet with Known Inductance and Current

[Sastronaut]

Homework Statement

an electromagnet is operated at 50A. assuming an inductance of 100H for the magnet's coil, what voltage will be developed when the switch is opened? when it is closed? assume that the switch requires 1 millisecond to operate.

Homework Equations

I(t) = Vb/(R(1-e^(-tR/L)))

The Attempt at a Solution

with the given formula above I am not quit sure how to proceed if I am not given resistance. any insight on how I should proceed with this problem would be great!

 

[nasu]

You could use Faraday's law of induction. It gives you the emf developed by a change in the magnetic flux.

 

[gneill]

Is there a circuit diagram to accompany this problem? Maybe that would give us a hint as to the where the resistance is supposed to be, or what might be in place to limit voltages, or what the implications are for a switch that "requires 1 millisecond to operate".

 

[Sastronaut]

no diagram but I figured it out.

di/dt = 50A/10^-7
V = L(di/dt)
V= 5MV

 

[Sastronaut]

thank you everyone!