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प्रश्न
Two bulbs are rated: bulb A 100W, 120 V bulb B 10 W, 120 V. If both are connected across a 120V supply, which bulb will consume more energy, When in parallel? Also calculate the current through each bulb in the above cases.
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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 Parallel:
Voltage is the same (120 V) across each bulb.
∴ The current in bulb A or IA = `"V"/"R"_"A" = 120/144 = 0.83` A
∴ The current in bulb B or IB `= 120/1440` = 0.083 A
Hence, power consumed in bulb A = PA = `"V"^2/"R"_"A" = (120 xx 120)/144`
= 100 W
and power consumed in bulb B = PB = `"V"^2/"R"_"B"`
`= (120 xx 120)/1440 = 10 "W"`
Hence, bulb A (100W, 120 V) consumes more energy then bulb B, when both are connected in parallel.
संबंधित प्रश्न
The table below shows the current in three different electrical appliances when connected to the 240 V mains supply:
| Appliance | Current |
| Kettle | 8.5 A |
| Lamp | 0.4 A |
| toaster | 4.8 A |
- Which appliance has the greatest electrical resistance? How does the data show this?
- The lamp is connected to the main supply by using a thin, twin-cored cable consisting of live and natural wires. State two reasons why this cable should not be used for connecting the kettle to the mains supply.
- Calculate the power rating of the kettle when it is operated from the 240 V mains supply.
- A main takes the kettle abroad where the mains supply is 120 V. What is the current is the kettle when it is operated from the 120 V supply?
The diagram above shows a circuit with the key k open. Calculate :
(i) the resistance of the circuit when the key k is open.
(ii) the current drawn from the cell when the key k is open.
(iii) the resistance of the circuit when the key k is closed.
(iv) the current drawn from the cell when the key k is closed.
An electric bulb of resistance 500 Ω draws current 0.4 A from the source. Calculate:
- the power of bulb and
- the potential difference at its end.
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.
An electric heater is rated 220 V, 550 W. Calculate the electrical energy consumed in 3 hours?
Find the heat produced in joules when a current of 10 amperes flows through a connecting wire of resistance 2 × 10-2 ohms and heating element of resistance 250 ohms for 2 seconds.
Find the energy released by a current of 0.25 amperes flowing through a heater for 5 minutes. The p.d. is 230 V.
