Three bulbs of ratings 40W, 60W and 100W are designed to work on 220V mains. Which bulb will glow most bright if they are connected in series 220V mains?
Answers
Given: Three bulbs of 40W, 60W and 100W are designed to work on 220V mains.
The current flowing in a series connection across each element in a circuit is same. Hence when bulbs of 40 W, 60 W and 100 W bulb are connected in series, the current flowing will be the same. Across all the three filaments, depending on resistance the voltage will be divided. When the wattage is higher, the resistance will be lower, so the 40 W bulb will have maximum resistance. Hence it will glow much brighter.
We have P = I^2 R where P is power . Power is higher for the bulb with high resistance which is 40 W bulb.
Thus 40 W bulb will glow brighter.
Given:
The power of three bulbs: 40, 60, 100 W
The voltage connected in series is 220 V
To find
Which bulb glow most bright.
Solution:
The formula of power
P=V²/R
For P=40 W
R(1)= 220×220/40= 1210 ohm
For P= 60 W
R(2)= 220×220/60=806.66 ohm
For P= 100 ohm
R(3)=220×220/100=484 ohm
The bulb having the highest brightness whose resistance is high.
So the correct answer is 40 W