# Motional emf

1. Oct 25, 2008

### goWlfpack

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

A square, single-turn wire loop 1.00 cm on a side is placed inside a solenoid that has a circular cross section of radius 3.00 cm, as shown in the figure below. The solenoid is 16.0 cm long and wound with 95 turns of wire.

(a) If the current in the solenoid is 3.00 A, find the flux through the loop.
T · m2

(b) If the current in the solenoid is reduced to zero in 4.00 s, find the magnitude of the average induced emf in the loop.
V

2. Relevant equations

EMF=-N mflux/delta t

where N is the number of turns

3. The attempt at a solution
im just having trouble manipulating the equation to get my unknowns....

2. Oct 25, 2008

### Staff: Mentor

First things first: What's the field inside the solenoid?

3. Oct 25, 2008

### goWlfpack

given as B=constant(current)/2R
6.3e-7?

4. Oct 25, 2008

### Staff: Mentor

You'd better look up the formula for the field within a solenoid.

5. Oct 29, 2008

### goWlfpack

ok i found the magnetic field inside the solenoid. it is B=(Moconstant)(I)(N/l)
where N is the number of turns and l is the length
this comes to .00224
so then i tried to multiply it by the area of the soleniod and i got the wrong answer.
so i tried it multiplied by the area of the square loop inside the soleniod and that was also a red x......
any help?

6. Oct 29, 2008

### Staff: Mentor

Looks OK.
That was a mistake, since you need the flux through the square loop.
That should work. Is the loop oriented perpendicular to the field or is it at some other angle? What did you use for the area of the loop?

7. Oct 29, 2008

### goWlfpack

yea sorry minor mathmatical error. I got it now! thanks for all the help! :)