Three bulbs of rating 40 watt 60 watt and 100 watt are designed to work on 220 volt mains.which bulb will glow most bright if they are connected in series across 220 volt mains
Answers
If three bulbs rated at 40W, 60W, and 100W are connected in a series at a 200V source, which bulb glows as brightly as the power?
Rating of bulbs hasn't been specified which is very important. Assuming each bulb is rated at 120V supply when connected across rated voltage i.e.120V supply then power dissipation across bulb will be 40W (or 100W). Rating is important because if 40W bulb rated at 120V supply is connected across 200V supply then it will not work (might burn or blow up), meaning a device can not work at a voltage much higher than its rated voltage.
Resistance of bulb is inversely proportional to its rated power, at same voltage because
P=(V*V)/R
Therefore R (40W bulb) > R (60W bulb) > R (100W bulb). Hence the bulb across which power dissipation is more will glow brighter.
When connected in series: In a series connection, current flowing across each element in circuit is same. So when 40W bulb, 60W bulb and 100W bulb are connected in series, same current will flow through them. The power dissipation across each of them will determine which bulb will glow brighter. From the relation P=(I*I) R, since current is same the power dissipation will be higher for the bulb with higher resistance i.e. 40W bulb.
Hence 40W bulb will glow brighter in series connection.
Answer:
40watt bulb will glow brightest