What Determines the Rate at Which Energy is Delivered by a Current? - Science


What determines the rate at which energy is delivered by a current?



The rate of consumption of electric energy in an electric appliance is called electric power. Hence, the rate at which energy is delivered by a current is the power of the appliance.

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Chapter 12: Electricity - Intext Questions [Page 220]


NCERT Science Class 10
Chapter 12 Electricity
Intext Questions | Q 1 | Page 220

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Define Electric power

Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?

1 calorie =  _________ joule.

If a bulb of 60W is connected across a source of 220V, find the current drawn by it.

Name the quantity whose unit is (i) kilowatt, and (ii) kilowatt-hour.

What is the meaning of the symbol kWh? Which quantity does it represent?

An electric kettle connected to the 230 V mains supply draws a current of 10 A. Calculate:

(a) the power of the kettle.
(b) the energy transferred in 1 minute.

The diagram below shows a circuit containing a lamp L, a voltmeter and an ammeter,. The voltmeter reading 3 V and the ammeter reading is 0.5 A. 


 What is the resistance of the lamp?
 What is the power of the lamp?

An electric heater is rated at 2 kW. Electrical energy costs Rs 4 per kWh. What is the cost of using the heater for 3 hours?

(a) Rs 12
(b) Rs 24
(c) Rs 36
(d) Rs 48

An electric kettle for use on a 230 V supply is rated 3000 W. For safe working, the cable connected to it should be able to carry at least: 

(a) 2 A
(b) 5 A
(c) 10 A
(d) 15 A

Why is an electric light bulb not filled with air? Explain why argon or nitrogen is filled in an electric bulb.

In a filament type light bulb, most of the electric power consumed appears as:

(a) visible light
(b) infra-red-rays
(c) ultraviolet rays
(d) fluorescent light

Name the S.I unit of electrical energy. How is it related to Wh?

A resistor of resistance R is connected to an ideal battery. If the value of R is decreased, the power dissipated in the resistor will ______________ .

A current passes through a resistor. Let K1 and K2 represent the average kinetic energy of the conduction electrons and the metal ions, respectively.

A bulb with rating 250 V, 100 W is connected to a power supply of 220 V situated 10 m away using a copper wire of area of cross-section 5 mm2. How much power will be consumed by the connecting wires? Resistivity of copper = 1.7 × 10−8 Ωm

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?

A servo voltage stabiliser restricts the voltage output to 220 V ± 1%. If an electric bulb rated at 220 V, 100 W is connected to it, what will be the minimum and maximum power consumed by it?

An electric bulb marked 220 V, 100 W will get fused if it is made to consume 150 W or more. What voltage fluctuation will the bulb withstand?

An immersion heater rated 1000 W, 220 V is used to heat 0.01 m3 of water. Assuming that the power is supplied at 220 V and 60% of the power supplied is used to heat the water, how long will it take to increase the temperature of the water from 15°C to 40°C?

The coil of an electric bulb takes 40 watts to start glowing. If more than 40 W are supplied, 60% of the extra power is converted into light and the remaining into heat. The bulb consumes 100 W at 220 V. Find the percentage drop in the light intensity at a point if the supply voltage changes from 220 V to 200 V.

Name the commercial unit of electrical energy.

Can you produce electricity from magnetism?

An electric iron rated 750 W is operated for 2 hours/day. How much energy is consumed by the electric iron for 30 days?

Point out two main disadvantages of ‘Tree System’.

Name two common material used for heating elements.

How does the heat produced by die passage of current in a metallic wire depend on the resistance of the wire.

How does earthing prevent electrical shock?

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.

An electric bulb is rated as 100W – 250V. What information does it convey? Calculate the resistance of its filament while glowing.

A bulb is connected to a battery of e.m.f. 6V and internal resistance 2Ω A steady current of 0.5A flows through the bulb. Calculate the resistance of the bulb.

A 100-watt electric bulb is used for 5 hours daily and four 60 watt bulbs are used for 5 hours daily. Calculate the energy consumed (in kWh) in the month of January.

A torch bulb is rated at 3 V and 600 mA. Calculate it’s

  1. power
  2. resistance
  3. energy consumed if it is used for 4 hours.

To minimise the power loss in the transmission cables connecting the power stations to homes and factories, the transmission cables carry current ______.

Electric power is inversely proportional to ____________.

A family uses 8 kW of power. Direct solar energy is incident on the horizontal surface at an average rate of 200 W per square meter. If 20% of this energy can be converted to useful electrical energy, how large an area is needed to supply 8 kW?

If a heater coil rated lkW, 220 V is connected in series with an electric bulb of 100 W, 220 V and are supplied 200V, power consumed by the bulb in this circuit is ______.

The average work done by a human heart while it beats once is 0.5 Joule. The power used by heart if it beats 72 times in a minute:

A electric bulb is rate 220 V, 60 W. its electric cell resistance is nearly

The electrical power and current in the circuit relates by ______

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]`

In the given figure, the emf of the cell is 2.2 V, and if internal resistance is 0.6 Ω. Calculate the power dissipated in the whole circuit.

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.

Using a long extension cord in which each conductor has a resistance of 8Ω, a bulb marked as '100 W, 200 V' is connected to a 220 V dc supply of negligible internal resistance as shown in the figure. The power delivered to the bulb is ______ W.


A conductor of 10 Ω is connected across a 6 V ideal source. The power supplied by the source to the conductor is ______.


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