Question

Resistance of one carbon filament and one tungsten lamp are measured individually when the lamp are lit and compared with their respective resistances when cold. Which one of the following statements will be true

• A. Resistance of the carbon filament lamp will increase but that of the tungsten will diminish when hot
• B. Resistance of the tungsten filament lamp will increase but that of carbon will diminish when hot
• C. Resistances of both the lamps will increase when hot
• D. Resistances of both the lamps will decrease when hot

Answer 1

Answer: (B)

Resistance of the tungsten filament lamp will increase but that of carbon will diminish when hot

Answer 2

R_conductor ∝ Temperature

and R_{semiconductor} ∝$\frac{1}{\text{Temperature}}$