# Homework Help: Finding the inductance

1. Oct 9, 2009

### JDiorio

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

An inductor has the form of a coil with 2074 turns and a diameter of 1.9 mm . The inductor is placed in a magnetic field perpendicular to the plane of the coil and increasing at a rate of 0.48 T/s . The current in the inductor is zero at t = 0, and then increases to 6.9 mA at t = 1.0 s. What is the inductance?

2. Relevant equations

This is the problem, I am obviously missing something.
I want to use the equation L= (u*N^2*A)/length.. but as you can see I am not given the length. I do not know how to incorporate the charge into finding the inductance.

3. The attempt at a solution
I feel like I am close. I am trying to use the increase rate of the magnetic field to find the emf, and then use the emf and the current to find the inductance, but then i get stuck.

2. Oct 9, 2009

### JDiorio

Re: Inductance

So I found the formula emf= -L ( dI/dt) where d = change in. How do I derive the emf from the information given. Also, this formula does not involve the number of turns nor does it involve the diameter.. so is this just extra information?

3. Oct 9, 2009

### rl.bhat

Re: Inductance

You can the equation as
emf = - NAdB/dt = L*di/dt. Or
NA(dB/dt)*dt = L*di
Take integration on both side and find L.

4. Oct 10, 2009

### JDiorio

Re: Inductance

is there anyway to do this problem without calculus? This is a non-calc based class so i have no clue how i would go about taking the integral..

5. Oct 10, 2009

### rl.bhat

Re: Inductance

In the given problem, dt is given(1s). di is given(6.9 mA). Substitute in the formula to get the inductance. No need to take integration.

6. Oct 10, 2009

### JDiorio

Re: Inductance

thanks a lot.. i finally got this stupid question.. really appreciate the help! thanks again..