question_answer

If the current through \[3\,\,\Omega \] resistor is 0.8 A, then potential drop through \[4\,\,\Omega \] resistor is :

A)  1.2V            

B)  2.6V

C)  4.8 V            

D)  9.6 V

Correct Answer: C

Solution :

Key Idea: In parallel combination of two resistors potential drop across each is same. In the given circuit, 30 and 6 0 resistors are in parallel, so potential drops across them will be equal. Let \[{{i}_{1}}\] and \[{{i}_{2}}\] currents are flowing in \[3\,\Omega \] and\[6\,\Omega \] respectively.                 \[\therefore \] \[3\,{{i}_{1}}=6\,{{i}_{2}}\] But \[{{i}_{1}}=0.8\,A\] (given) \[\therefore \] \[3\times 0.8=6{{i}_{2}}\] \[\Rightarrow \] \[{{i}_{2}}=\frac{3\times 0.8}{6}=0.4\,A\] Net current through the circuit                 \[i={{i}_{1}}+{{i}_{ & 2}}\]                 \[=0.8+0.4=12.\,A\] This current will flow through \[4\,\,\Omega \] resistor. So, potential drop across \[4\,\,\Omega \]. resistor is \[V=iR=1.2\times 4=4.8\,V\].