Question

An electric bulb having resistance 220 ohms glows with full brightness

Answer 1

Light bulbs are made to operate at particular voltage range and each having particular power output.If we take the rates range of both the bulb be 220 volts then,Resistance of 25 watt bulb = V^2/ R = 220^2 /25 = 1936 ohmSimilarly resistance of 100 watt bulb is 484 ohms.Now for a bulb to grow brighter it has to dissipate more power that is I^2*R should be more . Using this conclusing.SERIESIn series the current through both the bulb will be same so the bulb with higher resistace will grow brighter i.e the 25 watt bulb.ParallelIn parallel the voltage is same across the two and current through the 25 watt bulb will be less than that of 100 watt bulb as it's resistance is high. HENCE the bulb with power resistance will glow brighter i.e the 100 watt bulb.