1) A wire of length 1m is moving at aspeed 2m/sec perpendicular to a magnetic field of induction of 0.5T.The ends of wires are formed by a circuit of total resistance 6ohm.What is the rate at which work is done to keep the wire moving with a constant velocity?
A. 1/2W B.1/3W C.1/6W D.1/5W
2)A thin conducting ring of radius r has an electric charge +Q. Find the increase in the tension of wire if a charge +q is placed at the center of ring.
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2 Answers
32..we consider an element Δl on the circumference..
charge on considered element is Δq=λΔl
force of interaction between considered element on ring and charge Q0 IS..
fe=Q0λΔl4Πε0r2
here Δl=rθ
fe=Q0λθ4Πε0r
2Tsin(θ/2)= fe
or, Tθ=Q0λθ4Πε0r
T=Q0λ4Πε0r
putting value of λ=q/2Πr
T=Q0q8Πε0r2
111)
Induced emf=Bvl....
Current in the wire = Bvlr
So power reqd to keep it moving with const. vel=B.v.Bvlr=16.
Thus c).