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 ?

Options

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

Answer

A

Explanation

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 ` .