Q.
Four wires of equal length 8 m are arranged as shown in the figure. Wires, 2, 3 and 4 are of equal cross sectional area and wire 1 is of half the cross section of these wires. By how much distance in metrepointer at point 5 must be moved to get null point?
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answer is 2.
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Detailed Solution
For getting null pointR1R3=R2R4 as R2=R4R1=R3Let the pointer at point 5 is moved to left by distance x to get nul point as shown in the figure. If resistance per unit length of wire 3 is r then that of wire 1 will be 2r.(8−x)2r=x×2r+8×r4x=8x=2m
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