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I was doing some bonus homework questions and hit a few snags along the way. Any help would be appreciated!

1) What is the direction of the force on a current carrying wire in a magnetic field if the current is toward the left on a page and the magnetic field is down the page?

For this one I was thinking that the force was down out of the palm of your hand but I wasn't sure.

2) What is the force on a 3.5m long wire that is carrying a 12A current if the wire is perpendicular to earth's magnetic field?

The thing that is screwing me up in this question is the lack of information given. I have the length and the current given, but to find the force magnetic I also need the magnetic field strength (B). I'm not quite sure how to figure it out without be given the three variables of magnetic force.

A galvanometer has a full-scale deflection when the current is 50.0 uA. If the galvanometer has a resistance of 1.0 kiloohms, what should the resistance of the multiplier resistor be to make a voltmeter with a full-scale deflection of 30.0V?

I thought that I was doing this one right but my answer didn't coincide with the one in the book. This is what I did:

V/I = R 30V / 50x10^-6 A = 6.0 x 10^5 ohms total

(1/Rtotal) - (1/R1) = (1/R2)

(1/600 Kohms) - (1/1 kohms) = 600/599 = (599/600ohms) which is wrong.

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# Homework Help: Magnetic Forces

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