In the fig above, XY is of length 1m, The value of R at balance point Z is
A.
3.0Ω
B.
13.3Ω
C.
15.0Ω
D.
30.0Ω
Correct answer is D
At null deflection, p.d across R = p.d across xz
p.d across 20Ω = p.d across zy
\(\frac{R}{20}\) = \(\frac{60}{40}\)
R = 30Ω