English Medium कक्षा १० - CBSE Question Bank Solutions

What is meant by "electric power"?

Write the formula for electric power in terms of potential difference and current.

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?

Define kilowatt-hour. 

 How many joules are there in one kilowatt-hour?

Calculate the cost of operating a heater of 500 W for 20 hours at the rate of Rs 3.90 per unit.

When an electric lamp is connected to 12 V battery, it draws a current of 0.5 A. The power of the lamp is:   

(a) 0.5 W
(b) 6 W
(c) 12 W
(d) 24 W

The unit for expressing electric power is: 

(a) volt
(b) joule
(c) coulomb
(d) watt

Which of the following is likely to be the correct wattage for an electric iron used in our homes? 

(a) 60 W
(b) 250 W
(c) 850 W
(d) 2000 W

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

The SI unit of energy is :

(a) joule
(b) coulomb
(c) watt
(d) ohm-metre

The commercial unit of energy is :

(a) watt
(b) watt-hour
(c) kilowatt-hour
(d) kilo-joule

How much energy does a 100 W electric bulb transfer in 1 minute?

(a) 100 J
(b) 600 J
(c) 3600 J
(d) 6000 J

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

How many joules of electrical energy are transferred per second by a 6 V; 0.5 A lamp? 

(a) 30 J/s
(b) 12 J/s
(c) 0.83 J/s
(d) 3 J/s

At a given time, a house is supplied with 100 A at 220 V. How many 75 W, 220 V light bulb could be switched on in the house at the same time (if they are all connected in parallel)?

State whether an electric heater will consume more electrical energy or less electrical energy per second when the length of its heating element is reduced. Give reasons for your answer.

The table below shows the current in three different electrical appliances when connected to the 240 V mains supply: 

1. Which appliance has the greatest electrical resistance? How does the data show this?
2. 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.
3. Calculate the power rating of the kettle when it is operated from the 240 V mains supply.
4. 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?

Name two gases which are filled in filament type electric light bulbs.

Explain why, filament type electric bulbs are not power efficient.