Inductance of a coil for a given emf and current change

[jena]

Hi,

My Question:

What is the inductance of a coil if the coil produces an emf of 2.50V when the current in it changes form -28.0 mA to 31.0 mA in 12.0 ms?

For this I know I will need to use this equation:

E=-M(delta I)/(delta t)

My problem is that I was wondering if coming up with a negative inductance is alright.

Thank You

 

[Tide]

No. The inductance is positive. The induced EMF opposes the increasing current (Lenz's Law) which means that E must be negative (-2.50 V) in your example.

 

[jena]

So this work is fine then

E=-M(delta I)/(delta t)
2.50 V=(-M((31*10^-3 A) - (-28*10^-3 A)))/(12*10^-3 s)
2.50 V= -M(4.92 A/s)
-M=.51 H
M=-.51 H

Thank You