Advertisements
Advertisements
प्रश्न
An electric bulb, when connected across a power supply of 220 V, consumes a power of 60 W. If the supply drops to 180 V, what will be the power consumed? If the supply is suddenly increased to 240 V, what will be the power consumed?
Advertisements
उत्तर
The resistance of a bulb that consumes power P and is operated at voltage V is given by
\[R = \frac{V^2}{P} = \frac{220 \times 220}{60} = 806 . 67 \Omega\]
(a) Now the supply drops to V' = 180 V.
So, the power consumed,
\[P' = \frac{V '^2}{R} = \frac{\left( 180 \right)^2}{806 . 67} = 40 W\]
(b) Now the supply increases to V" = 240 V. Therefore,
\[P'' = \frac{{V''}^2}{R} = 71 W\]
APPEARS IN
संबंधित प्रश्न
Name two safety devices which are connected to the live wire of a household electric circuit
What is the SI unit of (i) electric energy, and (ii) electric power?
An electric bulb is rated ‘100 W, 250 V’. What information does this convey?
Calculate the current through a 60 W lamp rated for 250 V. If the line voltage falls to 200 V, how is the power consumed by the bulb affected?
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.
An electric kettle is rated 2.5 kW, 250 V. Find the cost of running the kettle for two hours at Rs. 5.40 per unit.
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.
What are the two main systems of wiring commonly used in houses? Which of these systems mentioned by you is better and why?
Household wiring for lamp connections can either be done in parallel or in series.Which one would you prefer? Give a reason for your answer.
A device is used to transform 12 V a.c. to 200 V a.c. What is the name of this device? Name the principle on which it works.
An electric heater is rated 220 V, 550 W. Calculate the electrical energy consumed in 3 hours?
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.
An electric appliance is rated at 1000 W, 250V. Calculate:
(i) The electrical energy consumed by the appliance in 12 hour.
(ii) The cost of energy consumed at Rs. 1.20 per kWh.
How long would this appliance take to use 1 kWh energy when operated at 250 V?
Electric power is inversely proportional to ____________.
A room has AC run for 5 hours a day at a voltage of 220V. The wiring of the room consists of Cu of 1 mm radius and a length of 10 m. Power consumption per day is 10 commercial units. What fraction of it goes in the joule heating in wires? What would happen if the wiring is made of aluminium of the same dimensions?
`[ρ_(Cu) = 1.7 xx 10_(Ωm)^-8, ρ_(Al) = 2.7 xx 10^-8 Ωm]`
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.
