# A flat, square surface with side length

1. Oct 22, 2012

### Mdhiggenz

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

A flat, square surface with side length 3.00cm is in the xy-plane at z=0 .

Calculate the magnitude of the flux through this surface produced by a magnetic field

B=(0.150T)i+(0.350T)j-(0.500T)k

What I'am doing is I know that the magnetic flux= BAcos(theta)

So I multiply my vector B by 0.03m and get (0.0045)i+(0.0105)j, and z=0 so I can ignore that value.

Then they are asking for the magnitude, so √(0.0045)^2+(0.00105)^2= 0.00462Wb , however that is not giving me the correct answer, what am I missing?

Thanks
2. Relevant equations

3. The attempt at a solution

2. Oct 22, 2012

### Flipmeister

What angle theta are you using for the magnetic flux?

Also, what's the area of a square? Seeing as a Tesla is 1 Wb/m^2, multiplying by 0.03m should get you an answer of Wb/m, not Wb.

3. Oct 22, 2012

### Mdhiggenz

Theta is not given so I assumed it was just 0degrees

4. Oct 22, 2012

### Flipmeister

Theta is the angle between the "normal" line of your plane and the magnetic field lines. It would be 0 degrees if the magnetic field lines were parallel with the normal (therefore perpendicular), but this is not the case here. You'll have to find the angle from the vector you're given.

5. Mar 23, 2013

### mitchapalooza

Le Answer

Use the BAcos(theta) formula to find the flux. But since the Magnetic field vector is given, keep in mind that flux operates perpendicular to the field, so all you really have to do is calculate (B_k)(A)cos(90). And you'll be squaring that number and then taking the root so because you only have one term in the "magnitude finding" process, just drop the negative sign.

6. Mar 24, 2013

### Mdhiggenz

Lol I finished that class about 8 months ago. Thank you though

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