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Grade: 12
        A 25  w, 220v and a 500 w, 220 v bulb glow at normal brightness when connected across the terminal of a batteries. When they are connected in series across the same material, 500 W bulb glows dimly. How could this happen?
2 years ago

Answers : (2)

Pratikshya kafle
13 Points
							When bulb rated different powers are connected in series,Brightness is inversely proportional to power rated i.e bulb rated high power glows dimly and bulb rated less power glows brightly.Since 500w>25w, 500w bulb glow dimly.
2 years ago
106 Points
We have, Power, P = V2 / R   -----------------------------------> Eqn 1
where, V is the voltage and R is the resistance.
Eqn 1 tells that rated power of the bulb is inversely proportional its resistance.
Therefore, 25 W bulb has the highest resistance compared to 500 W bulb.
When they are connected in series, the same amount of current passes through both 25W and 500W bulb.
We have, Power, P = I2 R   --------------------------->Eqn 2
Since the current is same, the power dissipation will be higher for the bulb with higher resistance according to Eqn 2. 
We know that R(25W bulb) > R(500W bulb)
So, bulb with 25W will have more power dissipation and glows brighly whereas, 500W bulb will have least power dissipation and glows dimly.
Hope it helps.
Approve if u like it.
2 years ago
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