- #1
moenste
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Homework Statement
The diagram shows a rigid conducting wire loop connected to a 6.0 V battery through a 6.0 V, 3.0 W lamp. The circuit is standing on a top-pan balance. A uniform horizontal magnetic field of strength 50 mT acts at right angles to the straight top part of the conducting wire in the direction indicated in the diagram, i. e. into the paper. This magnetic field extends over the shadowed area in the diagram. The balance reads 153.860 g. Calculate (a) the force exerted on the conducting wire by the magnetic field, and (b) the new balance reading if the direction of the magnetic field is reversed.
Answers: (a) 1.3 * 10-3 N, (b) 1.54; 115 g.
2. The attempt at a solution
(a) F = B I L. First we find I = P / V = 3 / 6 = 0.5 A. Plug it into the F formula: F = (50 * 10-3) * 0.5 * (51 / 10 / 100) = 1.28 * 10-3 N. This part should be correct.
(b) This part I have large doubts. First of all, what does "The balance reads 153.860 g." mean? And second of all what does the answer "(b) 1.54; 115 g" mean?
There are two styles of representing numbers: (i) 1,000,000.00 -- one million and (ii) 1 000 000,00 -- also one million. The mass -- what does it mean? .860 is the faction? Or it is 153 860,00? Or 153,86?
I also don't understand the answer. If we need to find the mass, which is 115 g, then what is 1.54?
And finally, how do we find the new balance reading? As I understand, the direction of force was upwards (current is going from +, so current is going from left to right through the wire and field), the field was into the paper, so the force was directed upwards. And now when the field is out of paper, the force is directed downwards. But that's as far as I can go.
Maybe F = m g so m g = B I L? Why do we need the 20 mm though...