Advertisements
Advertisements
प्रश्न
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.
Advertisements
उत्तर
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.
संबंधित प्रश्न
An electric lamp is labelled 12 V, 36 W. This indicates that it should be used with a 1 V supply. What other information does the label provide?
The commercial unit of energy is :
(a) watt
(b) watt-hour
(c) kilowatt-hour
(d) kilo-joule
State and define the household unit of electricity.
What is the resistance, under normal working conditions of a 240 V electric lamp rated at 60 W? If two such lamps are connected in series across a 240 V mains supply, explain why each one appears less bright.
Two resistors A and B of 4 Ω and 6 Ω respectively are connected in parallel. The combination is connected across a 6 volt battery of negligible resistance. Calculate the power supplied by the battery.
What does the unit kilowatt hour measure? Define it.
Point out two main disadvantages of ‘Tree System’.
What do you understand by ‘earthing’? What are the advantages of earthing in a household electric circuit? Explain, how it is done?
You are required to connect a bulb, a fan and a socket outlet to the mains in one set A and an air-conditioner and a refrigerator to the mains in other set B. Will you recommend the wire of same thickness and same insulation in both? explain your answer.
The equation I2R seems to suggest that the rate of heating in a resistor is reduced if resistance decreases, whereas equation P = V2/R suggests just the opposite. How do you reconcile this problem?
