Advertisements
Advertisements
Question
Two bulbs are rated: bulb A 100W, 120 V bulb B 10W, 120 V. If both are connected across a 120V supply, which bulb will consume more energy, When in series? Also calculate the current through each bulb in above cases.
Solution
In the case of bulb A, Power: P = `"V"^2/"R"_"A"`
RA = `"V"^2/"P" = (120 xx 120)/100` = 144 Ω
i.e., Resistance (RA) of bulb, A = 144 Ω
Similarly resistance RB of bulb, B = `"V"^2/"P"`
`= (120 xx 120)/10 = 1440` Ω
When the bulb are connected in series:
R = RA + RB = 144 + 1440 = 1584 Ω
∴ Current in the circuit `= "V"/"R" = 120/1584 = 0.076` A
Being in series, the same current passes through both the bulbs.
Power consumed in bulbs A = PA = i2 RA = (0.076)2 × 144 = 0.8317 W
Power consumed in bulbs B = PB = i2 RB = (0.076)2 × 144 = 8.317 W
This clearly shows that PA < PB i.e., bulb B (10W, 120 V) consumes more energy when these are connected series.
APPEARS IN
RELATED QUESTIONS
Which of the following terms does not represent electrical power in a circuit?
A bulb is rated as 250 V; 0.4 A. Find its : (i) power, and (ii) resistance.
An electric bulb is rated ‘100 W, 250 V’. How much current will the bulb draw if connected to a 250 V supply?
An electric iron is rated at 750 W, 230 V. Calculate the electrical energy consumed by the iron in 16 hours .
Two electric lamps each rating 100 W, 110 V are connected in series to a 220 V power supply and two other electric lamps each of marking 100 W, 220 V are connected in parallel to the same power supply. Will anyone of the two combinations give more light than the other? Give a reason for your answer.
State relative advantages and disadvantages of ring system of wiring over the tree system.
An electrical appliance is rated 1500 W, 250 V. This appliance is connected to 250 V mains. Calculate:
(i) the current drawn,
(ii) the electrical energy consumed in 60 hours,
(iii) the cost of electrical energy consumed at Rs. 2.50 per kWh.
An overhead tank of capacity 10 k litre is kept at the top of building 15 m high. Water falls in tank with speed 5`sqrt2` m/s. Water level is at a depth 5 m below ground. The tank is to be filled in `1/2` hr. If efficiency of pump is 67.5% electric power used is ______ W.
