Goyal Brothers Prakashan solutions for अ न्यू अप्रोच टू आईसीएसई [अंग्रेजी] कक्षा १० chapter 8 - Electric Energy, Power and Household Circuits [Latest edition]

Define the term electric work.

State and define the SI unit of electric work.

Name three bigger units of electric work and state their magnitude.

1. State two practical units of electric energy.
2. Define each unit mentioned in (i).

500,000 J of energy is consumed in 500 s. What is the power consumed?

Express 20 Wh of energy in S.I. units.

Express kilowatt-hour in joules.

A current of 0.5 A flows through the filament of a bulb with a resistance of 500 Ω for 100 s.

1. What is the power of bulb?
2. What is magnitude of energy consumed by bulb in watt hours?

400,000 joules of energy is consumed by an electric heater in 400 s.

1. What is power of heater?
2. If the above energy is supplied at 200 V, what is the magnitude of current flowing through heater?
3. What is the resistance of the element of the heater?

Express watt-hour in joules.

Express kilowatt-hour in joules.

Which of the two units (watt-hour or kilowatt-hour) is used for selling electrical energy to domestic consumers?

Calculate the current flowing through an electric bulb, which consumes 2 kWh of electric energy in 5 hours, such that the resistance of the bulb is 400 Ω.

How do kilowatt and kilowatt-hour differ?

A power house generates 200 MW of power. If the generating e.m.f. 40,000 V, what is the magnitude of current produced?

A nichrome wire X with length (l) and cross-sectional area (A) is connected to a 10 V source and another nichrome wire Y with length (2l) and cross-sectional area `(A/2)`, is connected to a 20 V source.

(a) Compare the resistances of wires X and Y. [Given that the resistivity of nichrome is (ρ).]

(b) Compare the electrical power consumed by each wire.

(c) Compare the masses of these wires. (Given that the density of nichrome is d.)

(d) State true or false:

Wire X and wire Y both show the same rise in temperature in the same time.

A electrical appliance is rated 2000 W − 200 V. This appliance is connected to 200 V mains. Calculate:

1. Current drawn by the appliance.
2. Resistance offered by the appliance.
3. Electric energy consumed by the appliance in 10 hours.
4. Cost of the electric energy consumed at ₹ 7.50 per kWh.

A bulb has a resistance of 20 Ω and the p.d. across its terminals is V. If the bulb is used for t seconds, then the energy consumed by the bulb is:

A current I flows through a resistance R for the time 't', the electric energy consumed by the resistance is:

The unit for electric work in SI system is:

An electric appliance has a rating of 1000 W–200 V. The resistance of the element of the electric appliance is:

Kilowatt hour is commercial unit of ______.

Kilowatt hour and kilowatt are ______.

Which is not the commercial unit of power, based on the decimal system?

One mega watt is equal to ______.

If P is the power of an electric circuit such that R is its resistance, I is the current flowing through it and V is potential difference at the ends of electric circuit then:

One kilowatt hour is equal to ______.

Electric energy in kilowatt-hours (kWh) is equal to:

A heater draws a current of 5A at 220 V for 2 minutes. The energy released by heater in kilojoules is:

An electric bulb consumes 8640 J of energy while operating at 24 V for 30 min. The current drawn by the bulb is:

An electric kettle draws a current of 4 A for 5 min. If the resistance of its element is 100 Ω, the energy drawn by kettle in kilo joules is:

A soldering rod draws an energy of 86400 J in 8 min when the current flowing through its element is 6 A. The resistance of the heating element of the soldering rod is:

An electric bulb whose filament is of resistance 4 Ω operates at 12 V for 20 s. The energy released by the bulb is:

An electric device consumes 5760 J of energy in 1.0 minute when the p.d. at its ends is 24 V. The electrical resistance of the device is:

An electric heater draws a current of 5 A when the supply voltage is 200 V. The power of 5 such heaters will be:

An electric bulb is rated 500 W-250 V. The magnitude of the current of such a bulb is:

An electric geyser is rated 2000 W – 200 V and operates 2.0 hours daily. If the energy cost ₹ 7.50 per kWh, the weekly bill of the geyser is:

Assertion (A): An electric bulb is rated as 100 W–220 V.

Reason (R): If the bulb is lighted on a 220 V supply, the electric power consumed by it is 100 W (100 J/s).

Assertion (A): One watt is the electric power consumed when a current of 1A flows through a circuit having potential difference of 1 V.

Reason (R): One watt-hour (Wh) is the electrical energy consumed by an electrical appliance of power 1 W used for 1 h.

Assertion (A): The power generated at the generating station is directly transmitted to the consumers at 11 kV.

Reason (R): Before transmission of power from the generating station, its voltage is raised to reduce the loss of energy in the form of heat in the transmission line wires.

Assertion (A): Kilowatt hour is the commercial unit of electric energy.

Reason (R): When 1000 W of power is used it is called one kilowatt.

Assertion (A): Higher the resistance of a filament lamp, less is the energy consumed by it.

Reason (R): Higher resistance of filament reduces the magnitude of current in an electric circuit.

The amount of electric energy, which flows through a conductor in one ______ at a power of one watt is called one watt hour.

One kilowatt hour is equal to ______.

The electric energy is sold for domestic purposes in ______.

At fixed potential difference the electric energy flowing in a conductor is directly proportional to square of ______.

The product of electric charge flowing through a conductor and the potential differences at the ends of the conductor gives the magnitude of ______ flowing through conductor.

Match the statements in Column A with those in Column B.

A torch bulb of 4.5 V, draws a current of 0.3 A. If the bulb is switched on for 10 minutes, calculate the energy released by the bulb.

Calculate the energy released by a heater, which draws a current of 5 A at 220 V for 1 min.

An electric device consumes 8640 J of energy in 30 min, while operating at 24 V. Calculate the current drawn by the device.

An electric heater draws a current of 4 A and its element has a resistance of 40 Ω. If the heater is switched on for 8 minutes, calculate the energy released in kilojoules.

An electric kettle draws a current of 4 A for 2.5 min. If the resistance of its element is 100 Ω, calculate the electric energy drawn by the kettle in kilojoules.

A soldering iron draws an energy of 43200 J in 4 min, when the current flowing through its element is 6 A, calculate the resistance of its heating element.

An electric room heater has a resistance of 40 Ω and operates at 220 V for 10 min. Calculate the heat energy dissipated by it in kilojoule.

Calculate the heat energy given out by the filament of an electric bulb in 20 s, when its resistance is 4 Ω and the p.d. across its ends is 12 V.

An electric device gives out 5760 J of heat energy in 1 min, when current flows through it at a p.d. of 24 V. Find the resistance of the device.

Calculate the total power of 8 fans, if each of them draws a current of 0.5 A at a p.d. of 200 V.

An electric heater draws a current of 3.5 A at a p.d. of 250 V. Calculate the power of 4 such heaters.

An electric bulb is rated 500 W – 200 V. Calculate the magnitude of the current.

An electric heater of power 1000 W, draws a current of 5.0 A. Calculate the line voltage.

An electric bulb of resistance 500 Ω draws current 0.4 A from the source. Calculate:

1. the power of bulb and
2. the potential difference at its end.

An electric heater has a resistance of 40 Ω and draws a current of 4 A. Calculate : (a) its power (b) p.d. at its ends.

An electric heater with a power of 900 W has a resistance of 36 Ω. Calculate the magnitude of the current and the p.d. at its ends.

An electric heater is rated 750 W – 200 V. Calculate (a) resistance of the heating element (b) current flowing through it.

An electric motor of power 1000 W, operates at 250 V. Calculate the inductive resistance of the motor and current flowing through it.

An electric device operates at 24 V and has a resistance of 8 Ω. Calculate the power of the device and the current flowing through it.

An electric heater is rated 750 W – 200 V. Calculate (a) current flowing through it, (b) resistance of its element. (c) If the heater is used to heat 400 g of water at 20°C and switched on for 5 minutes, calculate the final temperature of the water. [sp. heat capacity of water is \[4.2\frac{\text{J}}{\text{g}^\circ\text{C}}\]].

An electric bulb is rated 200 W – 200 V. It is immersed in 200 g of oil (SHC 0.8 Jg⁻¹°C⁻¹) at 10°C. The bulb is switched on for 2 minutes. If all the electric energy is absorbed in the form of heat energy by the oil, calculate:

1. Current flowing through the bulb.
2. Resistance of the filament of the bulb.
3. Final temperature of the oil.

An electric kettle is rated 1000 W – 250 V. It is used to bring water at 20°C to its boiling point. If the kettle is used for 11 minutes and 12 seconds, calculate :

1. Current flowing through the element.
2. Resistance of the element of the kettle.
3. Mass of water in the kettle [SHC of water = 4.2 Jg⁻¹°C⁻¹]

Calculate the current flowing through a nichrome wire, immersed in 100 g of oil at 20°C, such that the final temperature of the oil rises to 80°C in five minutes, when the supply of e.m.f. is 10 V. [Sp. heat capacity of oil is 0.85 Jg⁻¹°C⁻¹]

Calculate the resistance of a nichrome wire, which will bring 200 g of water at 20°C to its boiling point in 7 minutes, when the current flowing through the wire is 4 A.

Calculate p.d. at the ends of a power source which, supplies current to a 4 ohm resistance wire for 20 minutes and raises the temperature of 400 g of water through 20°С.

Calculate the current flowing through an electric drill, connected to a 200 V supply, if it drills a hole in a metal plate of mass 500 g, such that its temperature rises from 10°C to 60°C in 5 minutes, assuming all the work done is converted into heat energy. [S.H.C. of metal 0.6 Jg⁻¹°C⁻¹]

A battery of 24 V and negligible internal resistance is connected to two resistors of 12 Ω and 6 Ω in parallel and then to a nichrome wire of resistance 2 Ω, immersed in 100 g of oil (sp. heat capacity 1.2 Jg⁻¹°C⁻¹) at 30°C. The current is switched on for 2 minutes.

1. Draw the circuit diagram of the arrangement.
2. Calculate the current flowing through the main circuit.
3. Current flowing through the 6 Ω resistor.
4. Final temperature of the oil.

The circuit diagram shows four dry cells with an e.m.f. 1.5 V and internal resistance 0.25 Ω connected to an external circuit. A 3 Ω wire is immersed in 20 g of water at 20°C. The current switched on for 6 minutes and 36 seconds. Calculate:

1. Reading shown by the ammeter
2. Current in the 1.5 Ω wire
3. Final temperature of water

A battery of 12 V and negligible internal resistance is connected to an external circuit consisting of three resistors of 6 Ω, 3 Ω and 2 Ω in parallel, which further connected to a resistance of 3 Ω in series to the battery. The 3 Ω resistance is immersed in 50 g oil of sp. heat capacity 0.8 Jg⁻¹°C⁻¹, when the temperature of the oil rises by 54°C.

1. Draw the labelled circuit diagram.
2. Calculate the value of the current in the main circuit.
3. Calculate the current flowing in 2 resistance in parallel.
4. Calculate the time for which the current is switched on.

An electric kettle is rated at 200 V and can bring a certain amount of water to its boiling point in 5 minutes. If it is connected to a voltage supply of 180 V, calculate the time in which the same amount of water will reach its boiling point.

An electric kettle rated 250 V can bring a certain amount of water to its boiling point in 8 min. If it is connected to a 200 V mains, calculate the time in which the water comes to its boiling point.

An immersion heating rod is rated at 220 V and can bring a certain amount of water to its boiling point in 15 min. When this immersion rod is actually connected to an electric circuit, it brings the water to a boil in 18.15 min. Calculate the line voltage.

An electric bulb is marked 100 W – 200 V, what information does it convey? How many joules of energy are consumed by this bulb in two hours? How long will it take for the bulb to consume two kilowatt-hours?

An electric oven is marked 1000 W – 200 V. Calculate:

1. The resistance of its element.
2. Energy consumed by the oven in `1/2` hour in joules.
3. Time, in which it will consume 15 kWh of energy.

An electric motor is rated at 2 HP – 250 V. Calculate:

1. Current flowing through it.
2. Energy consumed by it in one second.
3. Time in which it will consume 90 kWh of energy.

[1 HP = 750 W]

Calculate the monthly bill for a heater of resistance 50 Ω, which is used on 200 V mains, such that its daily use is for 4 h. The energy cost is ₹ 2.50 per kWh.

A geyser is rated 2000 W and operates 2 hours a day on 200 V mains. Calculate the monthly bill for running the geyser when energy costs ₹ 1.90 per kWh.

An electric oven with a resistance of 20 Ω draws a current of 10 A. It works 3 hours daily. Calculate the weekly bill when energy costs ₹ 1.50 per kWh. [Hint (P = I².R)]

An electric bulb draws a current of 0.8 A and works on 250 V on an average 8 hours a day. If energy costs ₹ 1.50 per board of trade unit, calculate the monthly bill.

Two bulbs of 60 W each and two coolers of 200 W each work on average for 4 hours a day. If the energy costs ₹ 3.50 per kWh, calculate the monthly bill and the minimum fuse rating when power is supplied at 200 V.

4 tube lights of 40 W each and 2 fans of 100 W each are connected to 200 V mains and operate on average for 8 hours a day. If energy costs ₹ 1.50 per kWh, calculate (a) monthly bill (b) minimum fuse rating.

An electric motor of 2 H.P. and two coolers of 500 W each operate on 250 V mains for 4 hours a day. If the energy costs ₹ 1.80 per kWh, calculate (a) weekly bill (b) minimum fuse rating. [Take 1 HP = 750 W]

An electric circuit operating at 250 V has following appliances connected in parallel and the energy cost ₹ 5.40 per kVAh.

1. 4 bulbs of 100 W each, working 8 hours a day.
2. Two room heaters of resistance 50 Ω each, working 2 hours a day.
3. Two air conditioners drawing a current of 8A, working 6 hours a day.
4. Three coolers of `1/3` H.P each, working 10 hours a day.
   1. Calculate the monthly bill
   2. Calculate the minimum fuse rating.

A boys hostel has following appliances when energy is supplied at 200 V and costs ₹ 5.25 per kWh.

1. 40 bulbs of 100 W each, working 8 hours a day.
2. 20 fans each drawing a current 0.8 A and working 15 hours a day.
3. Two T.V. sets, each offering a resistance of 200 Ω and working 4 hours a day.
4. Two electric motors of 1.5 H.P each and working 4 hours a day
   1. Calculate the monthly bill
   2. Amongst the fuse of 48 A and 50 A which one you will use and why?

An establishment receives electric energy at a rate of ₹ 4.50 per kWh at a p.d of 240 V. It uses the following appliances:

1. 20 tube lights of 40 W each working 10 h a day.
2. Two stereo systems, each drawing a current of 2A and working 4h a day.
3. Four ovens, each of resistance 24 Ω working 6 h a day.
4. Two cooling machines of 4 H.P each working 15 hours a day.
   1. Calculate the monthly bill
   2. Minimum fuse rating of the circuit

A bulb is rated 100 W – 250 V.

1. What information does the marking on the bulb convey?
2. What is the magnitude of the current drawn by the bulb when connected to 250 V mains?
3. What is the magnitude of the resistance of the bulb?
4. It is found that the actual resistance of the bulb is far more than the calculated value in (c). Give a reason.
5. If on the average bulb is used for 4 hours a day find the electric energy consumed by the bulb in 30 days in kWh.

Name the device used to increase the voltage at a generating station.

At what frequency is AC supplied to residential houses?

Name the wire in a household electrical circuit to which the switch is connected.

Calculate the quantity of heat produced in a 40 ⁡Ω resistor carrying a current of 5A in 5 minutes.

State the characteristics required in a material to be used as an effective fuse wire.

Which particles are responsible for the transmission of current in metallic conductors?

To which wire of a cable in a power circuit should the metal case of the geyser be connected?

To which wire should the fuse be connected?

1. Two sets A and B of two bulbs each glowing in two separate rooms. When one of the bulb of set A is fused, the other bulb cease to glow. But in the set B, when one bulb fuses, the other continues to glow. Explain, why does the phenomenon occur?
2. Why do we prefer arrangement in set B for house wiring?

Water in an electric kettle connected to a 220 V supply took 5 minutes to reach its boiling point. How long will it take if the supply voltage falls to 200 V?

A 100 W bulb and 60 W bulb are connected in parallel. The bulbs are switched on for 10 minutes. Calculate the energy consumed by the bulbs in S.I. units.

How does earthing offer protection?

Draw a diagram of ring main circuit for domestic distribution of electric power.

The image given below displays kilowatt-hour meter readings recorded at two distinct points in time.

Assuming a continuously running 2000 W air conditioner as the sole electrical device in use, calculate the time interval, in hours, between these two meter readings.

Explain briefly the function of the following in the household wiring a three pin plug.

Explain briefly the function of the following in the household wiring main switch.

A bulb is marked 100 W – 200 V and an electric heater is marked 1000 W – 200 V. Answer the following questions.

1. What is the ratio of resistance of filament of the bulb and the element of heater?
2. How does the power voltage rating of an electric appliance help us to decide the type of connecting wire (leads) to be used for it?
3. In the above mentioned devices in (b) which of the devices needs thicker wire?

An electric bulb is rated 240V-60W and is working at 100% efficiency.
(i) Calculate the resistance of bulb.
(ii) (a) Draw the circuit diagram.
(b) What is the rate of conversion of energy in each bulb?
(c) Total power used by the bulbs.

Draw two wiring diagrams of the dual control switch, both diagrams showing the combination turned ON.

Of the three connecting wires in a household circuit: Which two of the three wires are at the same potential? In which of the three wires should the switch be connected?

An electric heater of power 1 kW raises the temperature of 500 g of a given liquid from 25°C to 31°C in 2 minutes. Calculate:

1. Heat capacity of the liquid.
2. Specific heat capacity of the liquid.

Give two characteristic properties of a copper wire which make it unsuitable for use as a fuse wire.

In what unit does the electric meter in a house measure the electrical energy consumed? What is its value in S.I unit?

Why should switches always be connected to the live wire? Give one precaution that should be taken while handling switches.

Name the material of a fuse wire.

The diagrams (a) and (b) given alongside are plug and socket with arrows marked 1, 2, 3 and 4, 5, 6 respectively. Identify and write live (L), neutral (N) and earth (E) against the correct number on your answer sheet.

Name two safety devices that are connected to the live wire of a household electrical circuit and give one important function of each of these two devices.

An appliance with a metal covering, rated at 2 kW, 220 V, is to be connected in a circuit. Given below are four diagrams (P, Q, R and S) depicting different circuit configurations.

1. Identify the safest circuit.
2. Write two reasons, supported by mathematical calculations, where applicable, to justify your choice.

State the colour of household wires according to the new international standard.

Live wire

State the colour of household wires according to the new international standard.

Earth wire

State the colour of household wires according to the new international standard.

Neutral wire

Why does an electrical engineer recommend copper wires of various thicknesses for different rooms in a household circuit?

Why does the heating element of a heater become red hot, but the connecting wires remain cold?

A fuse wire is connected in ______ before the switch.

A switch in a circuit is always connected in the ______.

According to the old convention, the colour of the earth wire is ______.

According to new convention, the colour of live wire is ______.

Which is not a characteristic of a fuse wire?

In a three pin plug the live pin is ______.

In a household electric circuit all appliances are connected in ______.

An average lighting circuit of a poor family has a fuse rating of:

The household appliances are connected in parallel because:

The household appliances which frequently come in contact with human hands are earthed because:

Which is not used for the heating element of a heating appliance?

Which is not the choice of heating element of an electric appliance?

Which is not a property of the lighting element of an electric appliance?

Which is not a heating appliance?

Which is not a lighting appliances?

A switch is placed in:

A fuse is placed in:

Assertion (A): A fuse wire is the weakest point in the distribution of electric energy in a household circuit.

Reason (R): Fuse melts when an electric circuit is overloaded or short circuited.

Assertion (A): In a domestic circuit a fuse is placed ahead of switch in the live wire.

Reason (R): The arrangement cuts off the current in case the circuit is overloaded.

Assertion (A): When a room heater is switched on, its heating element gets red hot, but the connecting wires do not heat up.

Reason (R): Connecting wires are of more resistance than heating element.

Assertion (A): In a household circuit all appliances are connected in parallel.

Reason (R): Equivalent resistance in parallel is always less than individual resistances.

Assertion (A): The heating element of an electric oven is made of nichrome wire, but the filament of bulb is made of tungsten.

Reason (R): Tungsten expands less as compared to nichrome on plug heated.

A fuse wire is connected in ______ before the switch.

In an electric plug the live pin on the ______ side.

A fuse in an electric circuit has ______ melting point and high resistance.

The earth wire protects the user from electric shock, because the ______ melts instantly and breaks the circuit.

The heating element of an electric oven is made of nichrome or ______ as they do not expand appreciably when hot.

Match the statements in Column A with those in Column B.

Assertion: A switch will serve the purpose of making and breaking a circuit when it is connected to the neutral wire.

Reason: Neutral wire is at zero potential.

Redraw the diagram by linking points A, B, and C to points X, Y, and Z on the socket.

The diagram below shows a bulb connected by dual control switches. Observe the diagrams and answer the questions that follow.

1. Which of the above circuits will be able to switch ON or switch OFF the bulb using both switches?
2. At present, in which circuit is the bulb glowing?
3. If we interchange the L and N wires in circuit B, will the circuit work?