Reason (R): There will be no change in brightness of bulb if source is ideal and for non ideal source voltage drop across bulb decreases.
Solution:
When a heavy current appliance is switched on, it draws a large current from the power supply. For a non-ideal source with internal resistance, this increased total current causes a larger voltage drop across the internal resistance of the source (or wiring). Consequently, the terminal voltage supplied to other devices like the light bulb decreases. A lower voltage across the bulb reduces its power output (\(P = V^2/R\)) and thus its brightness. So, Assertion (A) is true. Reason (R) correctly states that brightness remains constant for an ideal source and that voltage across the bulb decreases for a non-ideal source, which explains the dimming. Thus, Reason (R) is true and explains Assertion (A).
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