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

Answer

B

Explanation

(b) 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 then it drawn a little lesser current. Conequently, the current through the electric bulb recovers. Hence, dimness of hte bulb decreases.