Current Electricity Charging Discharging Of Capacitors Question 180
Question: 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
Show Answer
Answer:
Correct Answer: B
Solution:
Resistance of CD arm = 2r cos 72o = 0.62r Resistance of CBFC branch $ \frac{1}{R}=\frac{1}{2r}+\frac{1}{0.62r}=\frac{1}{r}( \frac{2.62}{2\times 0.62} ) $
$ \frac{1}{R}=\frac{2.62}{1.24r} $ \ $ R=\frac{1.24r}{2.62} $ Equivalent $ R’=2R+r=2\times \frac{1.24r}{2.62}+r $
$ =r,( \frac{2.48}{2.62}+1 )=1.946r $ Because the star circuit is symmetrical about the line AH \ Equivalent resistance between A and H $ \frac{1}{R _{eq}}=\frac{1}{R’}+\frac{1}{R’} $
Therefore $ R _{eq}=\frac{R’}{2}=\frac{1.946}{2}r=0.973r $
BETA
