Calculate the inductance of a coil of wire

[monnapomona]

Homework Statement

Calculate the inductance (SI units: Henries) of a coil of wire having a loop diameter of 0.5 cm and coil length of 10 cm. The wire has 1000 loops per meter.

Homework Equations

I think I can use this equation:
L= μₒAN² / x, x = length of wire, μₒ = 4π*10^-7 Tm/A
A = πr^2

The Attempt at a Solution

L= μₒ(πr^2)N² / x
= μₒ(π(0.0025 m)^2)*(1000^2) / 0.1 m
= 7.85 * 10^-5 H

But apparently on my homework assignment that is wrong. Am I using the wrong formula?

Edit: fixed units

 

[gneill]

Take a closer look at your value for N.

 

[monnapomona]

@ gneill: I'm not sure if I'm thinking about this correctly but since I was given 1000 loops per meter, would I have to multiply this by the length (0.1 m) in order to just get the number of loops (N)?

 

[gneill]

@ gneill: I'm not sure if I'm thinking about this correctly but since I was given 1000 loops per meter, would I have to multiply this by the length (0.1 m) in order to just get the number of loops (N)?

That would be logical, right?

 

[Nickie]

in equation

Your attempt at a solution is correct. It is possible that there is a mistake in the units given in the problem statement or a typo in the answer key. It would be worth double checking the units and calculations to make sure they are correct. If you are still unsure, you can always ask your instructor for clarification.