Example - Which lamp glow brighter?

By Bharat Ribadiya -
If 200w, 100 w and 60 w lamps connected in series with 230V AC , which lamp glow brighter? Each lamp voltage rating is 230V.

Each bulb when independently working will have currents (W/V= I)

For 200 Watt Bulb current (I200) =200/230=0.8696 A
For 100 Watt Bulb current (I100) =100/230=0.4348 A
For 60 Watt Bulb current (I60) =60/230=0.2609 A

Resistance of each bulb filament is (V/I = R)

For 200 Watt Bulb R200= 230/0.8696= 264.5 ohms
For 100 Watt Bulb R100= 230/0.4348 = 528.98 ohms and
For 60 Watt Bulb R60= 230/0.2609=881.6 ohms respectively

Now, when in series, current flowing in all bulbs will be same. The energy released will be I2R .

Thus, light output will be highest where resistance is highest. Thus, 60 watt bulb will be brightest. It has highest resistance & minimum current requirement. Highest voltage drop across it X I [which is common for all lamps] =s highest power.

Note to remember:

Lowest power-lamp has highest element resistance. And highest resistance will drop highest voltage drop across it in a Series Circuit And highest resistance in a parallel circuit will pass minimum current through it. So minimum power dissipated across it as min current X equal Voltage across =s min power dissipation.

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