Q.No.13.6: - Is the filament resistance lower or higher in a 500W, 220V light bulb than in a 100W, 220V bulb?

Q.No.13.6: - Is the filament resistance lower or higher in a 500W, 220V light bulb than in a 100W, 220V bulb?

Ans: -

Power of light bulb                    =        P₁       =        500W

Potential difference        =        V₁       =        220V

Now apply,

                                        P₁       =        V₁²/R₁

                                        R₁       =        V₁²/P₁

                                        R₁       =        (220)²/500

                                        R₁       =        48400/500

                                        R₁       =        96.8 Ω

For second Bulb

Power           P₂       =        100W

Voltage        V₂       =        220V

Now, 

                    R₂       =        V₁²/P₂

                    R₂       =        (220)₂/100

                    R₂       =        48400/100

                    R₂       =        484 Ω

It means that the filament resistance of 100W, 220V light bulb is higher than that of other.

Q.No.13.5: - What are the difficulties in testing whether the filament of a lighted bulb obeys Ohm’s law?

Q.No.13.5: - What are the difficulties in testing whether the filament of a lighted bulb obeys Ohm’s law?

Ans: - According to Ohm when we increase voltage then current will also increases in direct proportion but resistance of the conductor must remain same and hence temperature also must remain same or constant. But when we test the filament of a lighted bulb that either it obeys Ohm’s law or not then with the passage of time its temperature increases and resistance also increases. These are the difficulties in testing whether filament of a lighted bulb obeys Ohm’s law or not.