# Induced emf problem

1. Oct 9, 2009

### sandycow

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

A magnetic field is perpendicular to the plane of a single turn circular coil. The magnitude of the field is changing so that the emf of 0.80 V and a current of 3.2 A are induced in the coil. The wire is then re-formed into a single turn square coil, which is used in the same magnetic field (again perpendicular to the place of the coil and with the magnitude changing at the same rate). What emf and current are induced in the square coil?

2. Relevant equations
emf= ΔB/Δt*A

3. The attempt at a solution
I used the equation emf= ΔB/Δt*A. with the two areas πr^2 and 4r^2 and i thought that since they were in the same plane with the rate of change in the magnetic field the same, i could do this... 0.80V/πr^2 = emf of the square/ 4r^2 and then solve for the emf of the square since the radius cancels. my teacher gave us the answer and what i got was not correct so im not sure which equations im suppose to use to solve this?

2. Oct 9, 2009

### rl.bhat

Hi sandycow, welcome to PF.
Your calculation of the area of the square is wrong.
What is the circumference of the given circular coil? Straighten the wire, and reform it as a square. What will be the length of each side of the square? What is the area of the square?

3. Oct 9, 2009

### sandycow

ohhhhh. i get it haha thanks that was such an oversight.

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