Q. In a showing figure find the equivalent resistance between $A$ and $B$ .

2120 207 Rajasthan PMTRajasthan PMT 2002 Report Error

A

2/3 ohm

B

5/ ohm

C

8/9 ohm

D

7.5 ohm

Solution:

The figure can be shown as equivalent resistance of $R_{1}, R_{2}$ and $R_{3}$

$R^{'} = R_{1} + R_{2} + R_{3}$
$= 5 + 5 + 5 = 15 Ω$
Equivalent resistance of $R_{4}, R_{5}$ , and $R_{6}$
$R^{''} = 5 + 5 + 5 = 15Ω$
$R_{A B} = \frac{R ^{'} R ^{''}}{R ^{'} + R ^{''}}$
$= \frac{15 \times 15}{15 + 15} = \frac{15}{2}$
$= 7.5 o hm$