In the following star circuit diagram (figure), the equivalent resistance between the points A and H will be-

Options

A. 1.944 r
B. 0.973 r
C. 0.486 r
D. 0.243 r

Answer

B

Explanation

Resistance of CD arm = `2r cos 72^(@) = 0.62 r`
Resistance of CBFC branch `=1/R =1/(2r) + 1/(0.62r) =1/r (2.62)/(2 xx 0.62) = 2.113/r`
`rArr R = 0.47 r`
circuit is symmetrical about the line `DeltaH`
`R_(eq) = (2R + r)/2 = (2 xx 0.47r + r)/2 = (1.94 r)/2 = 0.973 r`