# Torque on a soleniod / coil

1. Oct 12, 2008

### jcvince17

Torque on a soleniod / coil in magnetic field

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

A solenoid having 180 turns and a cross-sectional area of 6.68 cm2 carries a current of 1.12 A

1) If it is placed in a uniform 1.12 T magnetic field, find the torque this field exerts on the solenoid if its axis is oriented perpendicular to the field.

2) If it is placed in a uniform 1.12 T magnetic field, find the torque this field exerts on the solenoid if its axis is oriented at 45.0* with the field

2. Relevant equations

τ = IBAsinθ

3. The attempt at a solution

1) know the following:
N=180 , B = 1.12T , I = 1.12A , θ = 90* , area = .0668 m2

τ = IBAsinθ

τ = (1.12 A) (1.12 T) ( .0668 m2) (sin90) = 0.084
I then take that and multiply by number of turns = 0.084 x 180 = 15.08

But my answer is wrong. where am I going wrong?

2) N=180 , B = 1.12T , I = 1.12A , θ = 45* , area = .0668 m2

τ = IBAsinθ

τ = (1.12 A) (1.12 T) ( .0668 m2) (sin45) = 0.060
I then take that and multiply by number of turns = 0.060 x 180 = 10.67

This is also a wrong answer. Where am I going wrong here?

Last edited: Oct 12, 2008
2. Oct 13, 2008

### alphysicist

Re: Torque on a soleniod / coil in magnetic field

Hi jvince17,

This area is not correct. Remember that the area given in the problem was in cm2, not cm. Do you see what it need to be?

3. Oct 13, 2008

### jcvince17

Re: Torque on a soleniod / coil in magnetic field

I sure do! thank you very much. I changed my area and recalculated and both answers are now correct!

4. Jan 9, 2012

### florence.noy

Good evening,

This is my first time doing this since i had just completed my registration. I am really very eager to know exactly my answer to the problem because when i tried solving it for number 1 my answer is (0) because i am using (cos 90) which is equal to 0. In number 2 my answer is 0.1066522483 N.m. I do not know if I am correct. If I am wrong please I need to know where did I get it wrong.

Thank you very much and more power to us!