question_answer

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

A)  2/3 ohm             

B)         5/ ohm

C)  8/9 ohm             

D)         7.5 ohm

Correct Answer: D

Solution :

The figure can be shown as equivalent resistance of \[{{R}_{1}},\]\[{{R}_{2}}\]and\[{{R}_{3}}\]                                 \[R={{R}_{1}}+{{R}_{2}}+{{R}_{3}}\]                                 \[=5+5+5=15\,\Omega \] Equivalent resistance of\[{{R}_{4}}{{R}_{5}}\]  and \[{{R}_{6}}\] \[\begin{align}   & R=5+5+5=15\Omega  \\  & {{R}_{AB}}=\frac{RR}{R+R} \\ \end{align}\] \[=\frac{15\times 15}{15+15}=\frac{15}{2}=7.5\,\text{ohm}\]