Assertion : An electric bulb becomes dim, when an electric heater in parallel circuit is switched on.
Reason : Dimness decreases after sometime.

Options

A. If both assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the assertion
C. If assertion is true but reason is false
D. If the assertion and reason both are false.

Answer

B

Explanation

The electric power of a heater is more than that of a bulb. As ,`P prop 1/R`, the resistance of heater is less than that of the electric bulb. When a heater connected in parallel to the bulb is switched on, it draws more current due to its lesser resistance, consequently, the current through the bulb decreases and so it becomes dim. When the heater coil becomes sufficiently hot, its resistance becomes more and then it draws a little lesser current. Consequently, the current through the electric bulb recovers.
Hence, dimness of the bulb decreases.