# Homework Help: A Rectangle Parallel to a Magnetic Field

1. Jul 19, 2011

### aximwolf

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

file:///Users/LabGuest/Desktop/CH26.tiff

2. Relevant equations

FB= qv cross B

3. The attempt at a solution

If the the rectangle is parallel to the magnetic field and we know that FB is perpendicular to the B field itself than there should be a net Torque but no net force. Is this assumption correct?

My first intuition was to say there was a net force and no net torque but I think that is wrong because magnetic force acts perpendicular to the magnetic field (B).
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

#### Attached Files:

• ###### CH26.gif
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128
2. Jul 20, 2011

### ehild

Yes, it is correct. Can you explain, why?

ehild

3. Jul 20, 2011

### aximwolf

Yes because Magnetic Force = qv cross B thus it acts perpendicular to the magnetic field (B) since it is a cross product. The magnitude of the force is qvbsin(theta).

4. Jul 20, 2011

### ehild

But then there can be a net force on the rectangle, perpendicular to it, is it right?

What is v in the formula?

ehild

Last edited: Jul 20, 2011
5. Jul 20, 2011

### cupid.callin

there is a different formula (derived from the formula u wrote) used in case of currents ... do you know it?

6. Jul 20, 2011

### WatermelonPig

I would consider the magnetic force on each segment of the loop and sum these.

7. Jul 20, 2011

### cupid.callin

correct way !!!