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Four wires of equal length 2 m are arran...

Four wires of equal length 2 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 pointer at point 5 must be moved to get null point ?

A

0.5m toward point 6

B

0.5 m toward point 7

C

1 m toward point 6

D

1 m toward point 7

Text Solution

Verified by Experts

The correct Answer is:
A
a. For getting null point
`R_1/R_3 = R_2/R_4 as R_2= R_4`
`R_1 = R_3`
Let the pointer at point 5 is moved
to left by distance x to get null point
as shown in the figure. If resistance
per unit length of wire 3 is r then
that of wire 1 will be 2r.
`(2-x) 2r = x xx 2r + 2 xx r`
or `4x = 2`
or `x = 2/4 = 0.5 m ` .
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