Electromagnetic question related to emf

[pokeefer]

Homework Statement

A generator consists of 250 turns of wire each with a radius of 8.7 cm. The armature turns with a frequency of 120 r/s in a magnetic field of 0.86 T

a.) What is the maximum emf generated? (4 marks)

b.) What is the average emf generated during the time interval while the armature is moving one quarter of a turn from a position where the flux through the armature is maximum? (4 marks)

c.) What is the average emf generated during one complete turn of the armature? Explain.
(4 marks)

Homework Equations

emf(max) = 2piefNAB
average emf = flux / time
average emf = BA / time
average emf = BLv
v = 2pie(r) / T

The Attempt at a Solution

Ok so for part (a) I got:

emf = 2piefNAB

emf = (6.28)(120)(250)(0.087)^2(0.86)
emf = 1226 V

I'm stuck on part (b) and (c)

Why am I stuck?

1.) Well I'm unsure what formula to use.

2.) I don't know how I can find the area. I only have the radius and I assumed the area is radius squared.

3.) If I use the other formula there would still be one unknown which is L (length)Can someone please give me the appropriate formula to use for parts (b) and (c) and not just worded hints?

I've got a physics test tommorow on electromagnetics.

 

[anathema]

For part (b), you can use the formula for average emf, which is flux divided by time. In this case, the flux through the armature is maximum when the armature is perpendicular to the magnetic field, so the flux would be the maximum flux, which is given by BA. The time interval would be the time it takes for the armature to move one quarter of a turn, which is 1/4 of the period of rotation (T). So the formula would be:

average emf = BA / (1/4 T)

To find the area (A), you can use the formula for the area of a circle, which is pi times the radius squared (A = pi*r^2).

For part (c), you can use the same formula for average emf, but this time, the time interval would be one complete turn, which is the period of rotation (T). So the formula would be:

average emf = BA / T

And again, you can use the formula for the area of a circle to find A.

Hope this helps! Good luck on your test tomorrow.