Question

A bulb is connected to an ideal battery of emf 10 V so that the resulting current is 10 mA . When the bulb is connected to 220 V mains (ideal), the current is 50 mA. choose the correct alternative

• A. the resistance of the bulb is 1 k ohm and in the second case, it is 4.4 k ohm
• B. it is not possible since ohm's law is not followed
• C. the increase in resistance is due to heating of the filament of the bulb when it is connected to 220 V main
• D. none of these

Answer 1

The correct option is A the resistance of the bulb is 1 k ohm and in the second case, it is 4.4 k ohm

A bulb is connected to an ideal battery of emf$=10V$

Current$=10mA=10\times {10}^{-3}A$

when the bulb connected $220V$ (main)

and current$=50\times {10}^{-3}A$

Using Ohm's law,

First case:

$R=\frac{10\times {10}^3}{10}=1K\Omega$

Second case

$R^{\prime }=\frac{220\times {10}^3}{50}=4.4k\Omega$

Hence answer $\left(A\right)$ will be correct.