# Area of a Circular Coil

1. Jul 27, 2014

### ikentrovik

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

I understand everything in this problem except I dont know how they got (1/4) in the area of a coil.

Can someone explain this? I have googled it and im not getting a clear answer.

I thought the area of a coil could be (pi(r)^2)L where l is the length. But wouldnt this be a cyclinder? How would I find it when the inner core of the cyclinder is missing?

Thank you

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2. Jul 27, 2014

### Orodruin

Staff Emeritus
The coil is circular. The area of a circle is $\pi r^2$ and r is half of the diameter. The expression you gave is not an area, it has dimensions length^3.

3. Jul 27, 2014

### ikentrovik

You are right. I guess I gace volume. What I really don't understand is why there is a (1/4). Could you please explain why? Thank you.

4. Jul 27, 2014

### Orodruin

Staff Emeritus
r = d/2 implies r^2 = d^2/4 ...

5. Jul 27, 2014

### ikentrovik

Oh ok thank you! What I did was divide the diameter in half right away. Thats why I was confused.