2. The device at right is known as a rail gun. The bar has a flat bottom and sli

Question

2. The device at right is known as a rail gun. The bar has a flat bottom and slides along the wires while maintaining good electrical contact. Assume that the wire has negligible resistance compared to the bar, which has resistance R 1 ohm. The magnetic field shown is externally applied and is uniform. (a) What is the magnetic force on the bar (magnitude and direction)? (b) The bar starts at rest, has a mass of 1 kg, and you may neglect friction. If the wire tracks are 10 m long and L 1 m apart, B 1 T, and V 20 volts, what is the bar's speed when it flies off the track? How much time does it spend on the track? (c) The bar should in fact have less resistance than the wire, because it has a L larger cross-section and shorter length. I told you to assume the bar has all the resistance just to make your calculations easier. How does the problem become more complicated if the wire has most of the resistance? Describe a plan for solving the problem in this case. There is no need to execute your plan in detail, but do predict how the result will differ.

Explanation / Answer

a) F=BIL=BLV/R Direction towards right....using fleming left hand rule.

b)I=V/R=20/1=20A

M=1kg

L=1m

S=10m

F=BIL=Ma

1*20*1=1*a

a=20m/s2

S=ut+1/2at^2

10=10t^2

t=1sec

c)as rod moves right effective length of wire decreases ans Resistance decreases which cause in increased current ....non uniform accelerated motion.it takes less time

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