# Magnetic field questionwhat did i do wrong

1. Mar 5, 2006

### kevinlikesphysics

4. [SFHS99 21.P.37.] A thin 1.00 m long copper rod has a mass of 50.0 g. What is the minimum current needed in the rod to cause it to float in a magnetic field of 1.00 T?

i got 4.9 what am i doing wrong i used ma =BiL

can someone tel me what im doign wrong

2. Mar 5, 2006

### Hootenanny

Staff Emeritus
I got:

$$mg = BIL$$
$$I = \frac{mg}{BL} \Rightarrow I = \frac{0.05\times 9.81}{1\times 1}$$

$$I = 0.4905 A$$

Same as you.
?????

Last edited: Mar 5, 2006
3. Mar 5, 2006

### physicsprasanna

why do you say the answer is wrong???

4. Mar 5, 2006

### topsquark

Well, in case it's escaped notice, Hootenanny's answer is 1/10 of kevinlikesphysics'. I'm assuming that kevinlikesphysics simply converted the 50.0 g incorrectly.

-Dan

5. Mar 5, 2006

### Hootenanny

Staff Emeritus
Ahhh, indeed. I miss read. I feel rather stupid now.