What is the Motional EMF in a Solenoid with a Square Loop Inside?

[goWlfpack]

Homework Statement

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

Homework Equations

EMF=-N mflux/delta t

where N is the number of turns

The Attempt at a Solution

im just having trouble manipulating the equation to get my unknowns...

 

[Doc Al]

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

 

[goWlfpack]

given as B=constant(current)/2R
radius is 3 so
6.3e-7?

 

[Doc Al]

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

 

[goWlfpack]

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

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?

 

[Doc Al]

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

Looks OK.

so then i tried to multiply it by the area of the soleniod and i got the wrong answer.

That was a mistake, since you need the flux through the square loop.

so i tried it multiplied by the area of the square loop inside the soleniod and that was also a red x...

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?

 

[goWlfpack]

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?

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