question_answer

An electric bulb rated as \[500\,\,W-100\,\,V\] is used in a circuit having \[200\,\,V\] supply. The resistance \[R\] that must be put in series with the bulb, so that the bulb draws \[500\,\,W\] is

A) \[100\Omega \]                               

B) \[50\Omega \]

C) \[20\Omega \]                                 

D)  \[10\Omega \]

Correct Answer: C

Solution :

We know that,\[P=Vi\] \[\therefore \]Current through the circuit,                 \[i=\frac{500}{100}=5\,\,A\] Potential difference across,\[R=100\,\,V\] \[\therefore \]Relation,\[V=IR\]                   \[100=5\times R\] \[\Rightarrow \]               \[R=\frac{100}{5}=20\Omega \]