Question

1/ If three 10 Watt light bulbs are connected in series to a 60V power supply, what is the current throught each bulb?

2/ If a 4th 10 Watt bulb is added in series, would each bulb burn brighter , dimmer, or remain in the same as before the bulb was added, and why?[Hint: consider what would happen to the current.]

Answer 1

1/ If three 10 Watt light bulbs are connected in series to a 60V power supply, what is the current throught each bulb?
resistance of a 10 Watt = v²/p = 60²/10 =360 ohm
If three 10 Watt light bulbs are connected in series then resistance = 3* 360 ohm = 1080 ohm
then current though these bulbs = 60/1080 = 0.0556 A

2/ If a 4th 10 Watt bulb is added in series, would each bulb burn brighter , dimmer, or remain in the same as before the bulb was added, and why?[Hint: consider what would happen to the current.]
If a 4th 10 Watt bulb is added in series, then current through the bulbs = 60/(4*360) = 0.0416 A
and voltage across the bulb = 60/4 =15V
power of the bulb = 15*0.0416 = 0.625 W
power of a bulb when there were 3 bulbs connected = (60/3)*0.0556 = 1.11 W
so In newly connected circuit each bulb burn dimmer