question_answer

In circuit shown below, the resistances are given in ohms and the battery is assumed ideal with emf equal to 3 volt. The voltage across the resistance R4 is [UPSEAT 2004; Kerala PMT 2004]

A)         0.4 V

B)         0.6 V

C)         1.2 V

D)         1.5 V

Correct Answer: A

Solution :

                                         Equivalent resistance of the given network \[{{R}_{eq}}=75\,\Omega \] \ Total current through battery \[i=\frac{3}{75}\] \[{{i}_{1}}={{i}_{2}}=\frac{3}{75\times 2}=\frac{3}{150}\] Current through \[{{R}_{4}}=\frac{3}{150}\times \frac{60}{(30+60)}\]\[=\frac{3}{150}\times \frac{60}{90}=\frac{2}{150}A\] \[{{V}_{4}}={{i}_{4}}\times {{R}_{4}}=\frac{2}{150}\times 30=\frac{2}{5}V=0.4\,V\]