Question

Assertion (A): A torch bulb when cold has a resistance 1 Ω and it draws a current 300 mA. When glowing from a source of potential difference 3 V, the resistance of the bulb is 10 Ω.

Reason (R): Resistance of the filament of the bulb increases with the decrease in temperature.

पर्याय

• Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).

• Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).

• Assertion (A) is false, but Reason (R) is true.

• Assertion (A) is true, but Reason (R) is false.

Answer 1

Assertion (A) is true, but Reason (R) is false.

Explanation:

When the bulb glows, V = 3 V and I = 300 mA = 0.3 A

So R = `V/I`

= `3/0.3`

= 10 Ω

Thus, the assertion is true.

For a metallic filament, resistance increases when temperature increases, not when temperature decreases. So the reason is false.