If 25W, 220 V and 100 W, 220 V bulbs are connected in series across a 440 V line, then(a) only 25W bulb will fuse(b) only 100W bulb will fuse(c) both bulbs will fuse(d) None of these
Answers
25 W is the correct answer .
Answer:
Explanation:
Both the bulbs has a voltage rating is 220 V, thus voltage remains constant in both the cases. The bulb that has a lower power rating will have higher resistance, whereas both the bulbs are connected in series. Hence, both the resistances will combine into one.
Resistance= Voltage²/ Power
R-25= 220²/25=1936 Ohms.
R-100= 220²/100 = 484 Ohms.
Since, both the bulb are in series, total resistance = 1936+484 =2420 Ohm
Voltage=Current×Resistance
For 440 V, current is:
440 V/2420 Ohm= 0.1818 Amp
Voltage across 25 W bulb will be = Current × resistance of 25W bulb
= 0.1818 × 1936 = 352 Volts.
Voltage across 100 W bulb will be =Current × resistance of 100 W bulb
= 0.1818 × 484 = 88 Volts
In a series connection, the equipment with higher resistance have to bear more voltage. Thus, the 25W bulb will fuse first.