# Selina Concise Class 10 Physics Chapter 9 Household Circuits Solution

## Selina Concise Class 10 Physics Solution Chapter No. 9 – ‘Household Circuits’ For ICSE Board Students. Selina Concise Class 10 Physics Chapter 9 Household Circuits Exercise All Questions and Answers by Physics Teacher here in this post.

#### Exercise 9(A)

Question: 1

At what voltage and frequency is the electric power generated at the power generating station?

Solution: 11kV and 50Hz is the voltage and the frequency of the electrical power generate at the power generating station.

Question: 2

(a) At what voltage is the electric power from the generating station transmitted? Give reasons for your answer.

(b) What is the nature of the current transmitted from the power station?

Solution:

a.) The electric power station generates 11 kV voltage as lower voltage can produce very high current. Producing power more than 11kV can cause insulation difficulties.

b.) The power station transmits AC, alternating current.

Question: 3

The voltage of power generated at the generating stations is first stepped up before its transmission. Give reason.

Solution: The voltage of power generated at generating stations is stepped up cause energy loss is unavoidable while transmitting it for long distance. The resistance of the wire cause loss of energy hence the power generated at power station is stepped up from 11 kV to 132kV using step-up transformer.

Question: 4

Explain with the aid of a simple diagram, the transmission of electric power from the generating station to your house.

Solution: Question: 5

At what voltage and frequency is the a.c. supplied to our houses?

Solution: the voltage and frequency of A.C. current provided is 220V and 50Hz respectively.

Question: 6

Name the device used to (a) Increase the voltage at the generating station (b) Decrease the voltage at the sub-station for its supply.

Solution:

a.) Step-up transformer.

b.) Step-down transformer.

Question: 7

(a) Name the three connecting wires used in a household circuit.

(b) Which two wires mentioned in part (a) are at the same potential?

(c) In which of the wire stated in part (a) the switch is connected?

Solution:

a.) Neutral wire, live wire and earth wire

b.) Neutral wire and earth wire.

c.) Live wire where switch is connected.

Question: 8

What is the pole fuse? Write down its current rating.

Solution: While connecting the connection from pole to meter of the house a fuse of high rating is connected to live wire just before the meter or at the pole. This fuse is called as pole fuse. The current rating of the fuse is 50A.

Question: 9

State the function of each of the following in a house circuiting:

(a) kWh meter, (b) the main fuse, and (c) the main switch

Solution:

a.) The cable is connected to kWh meter after the company fuse. Connection is made to main switch from this fuse.

b.) Fuse is connected to live wire, which is used to trip the connection when high current flowing through circuit.

c.) Main switch connects both live and neutral wire and used to disconnect from main supply.

Question: 10

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

Solution: The electric meter in a house measured in kWh.

1 kWh = 3.6 x106J is the S.I. unit.

Question: 11

Where is the main fuse connected in a house circuit?

Solution: Main fuse is connected to live wire before main switch in the connection board of a house circuit.

Question: 12

State one advantage of using the main switch in house wiring.

Solution: The main switch is simultaneously used to break connection of live wire and neutral wire. Which helps in protecting appliances from accidental damage.

Question: 13

Draw a circuit diagram to explain the ring system of house wiring. State two advantages of it.

Solution: Advantage of this system is every appliance has separate fuse and its cheaper than other methods.

Question: 14

Draw a labelled diagram with the necessary switch, regulator, etc. to connect a bulb and a fan with the mains. In what arrangement are they connected to the mains: series or parallel?

Solution: System is connected in parallel.

Question: 15

How should the several electric lamps be connected with the mains so that the switching on or off a lamp has no effect on the operation of other lamps?

Solution: All electrical appliances in a building should be connected in parallel to the main. Electrical appliance should be connected to separate switch and separate fuse so that the switching on or off a lamp has no effect on the operation of other lamps.

Question: 16

Fig.9.12 shows three bulbs A, B and C each of rating 100 W, 220 V connected to the mains of 220 V. Answer the following:

(a.) How is the bulb A connected with the mains? At what voltage does it glow?

(b.) How are the bulbs B and C connected with the mains? At what voltage does the bulb B glow?

(c.) How is the glow of bulbs A and C affected if bulb B gets fused?

(d.) How is the glow of bulbs B and C affected if bulb A gets fused?

Solution:

a.) Bulb A is connected in parallel with mains. Bulb glows at 220 V.

b.) Bulb B and C are connected in series to main. So the voltage gets divided hence bulb B will glow at 110 V.

c.) As bulb B gets fused bulb A will not get affected as it is in parallel, and C  will not glow as it is connected in series to B.

d.) Bulb B and C will not get affected if bulb A gets fused.

Question: 17

Two sets A and B each of four bulbs are glowing in two separate rooms. When one of the bulbs in set A is fused, the other three bulbs also cease to glow. But in set B, when one bulb fuses, the other bulbs continue to glow.

(i.) Explain the difference in the two sets,

(ii.) Which set of arrangement is preferred in the housing circuit and why?

Solution:

i.) as in set A the fusing of one bulb affects the other this set of bulb is connected in series. While in set B bulbs are connected in parallel hence they operate at independent voltage hence fusing of one bulbwill not affect other three.

ii.) Set B or the parallel arrangement is preferred in household circuits as the appliances don’t have share voltage and can operate independently.

MULTIPLE CHOICE TYPE

Question: 1

The main fuse is connected in:

(a) Live wire

(b) Neutral wire

(c) Both the live and earth wires

(d) Both earth and the neutral wire.

Solution: (a) live wire

Question: 2

The electrical appliances in a house are connected in:

(a) Series

(b) Parallel

(c) Either in series or parallel

(d) Both in series and parallel

Solution:(b) Parallel

Question: 3

The electrical meter in a house records the consumption of:

(a) Charge

(b) Current

(c) Energy

(d) Power

Solution:(c) Energy

#### Exercise 9 (B)

Question: 1

What is a fuse? Name the material of fuse. State one characteristic of the material used for fuse.

Solution: A safety device used to limit the current in the circuit which is connected to live wire is called as fuse.

Alloy of lead and tin is used as fuse wire as it has more specific resistance and low melting point.

Question: 2

Name the device used to protect the electric circuits from overloading and short circuit. On what effect of current does it work?

Solution: Fuse is used to protect the electric circuits from overloading and short circuit. Fuse is based on heating effect of the current.

Question: 3

Complete the following sentences:

(a.) A fuse is a short piece of wire of high _________ and of material low _________.

(b.) A fuse wire is made of an alloy of ________ and ________. If the current in a circuit exceeds the current rating of the fuse wire it _________.

(c.)A fuse is connected in ________ with the ________ wire.

(d.) Higher the current rating, _______ is the fuse wire.

(e.) Live wire is also called __________ wire.

Solution:

(a.) resistance, low melting point.

(c.) series, live wire.

(d.) thicker

(e.) phase wire.

Question: 4

Why is the fuse wire fitted in a porcelain casing?

Solution: fuse wire is fitted in a porcelain casing as porcelain is a bad conductor of electricity.

Question: 5

How is a fuse put in an electric circuit? State the purpose of using a fuse in a circuit.

Solution: Fuse is put in an electric circuit in series with live wire. Th purpose of using a fuse in a circuit is to safeguard the circuit from excessive current the circuit. Question: 6

Describe with the aid of a diagram some form of a fuse, which is used in the electric lighting circuit of a house. Give two reasons why a fuse must not be replaced by an ordinary copper wire.

Solution: Ordinary copper wire won’t cut the electrical circuit in presence of high electrical charge as its melting point is very high.

Question: 7

A fuse is always connected in the live wire of the circuit. Explain the reason.

Solution: fuse is connected to live wire because when current in circuit increases the fuse trips the connection and saves the appliances and human from getting fatal electric shock. But if the fuse is not connected to live wire except if its connected to neutral wire and fuse trips the connection will be broken as the live wire is connected to the appliances and it risks the chance of getting electrocuted by that appliance.

Question: 8

How does the (i) thickness and (ii) length of a fuse wire depend on its current rating?

Solution:  Current rating is directly proportional to the thickness of wire and is independent of length of the wire.

Question: 9

Two fuse wires are rated 5 A and 20 A. Which of the two is (i) thicker, (ii) longer?

Solution: As current rating is directly proportional to the thickness of wire and is independent of length of the wire. 20A wire is thick and 5 A wire is thin. And we can’t predict length based on the current rating.

Question: 10

Explain the meaning of the statement ‘the current rating of a fuse is 5 A’

Solution: Current rating of a fuse is 5 A means fuse will trip the circuit if the current exceeds above 5 A.

Question: 11

‘A fuse is rated 8 A’. Can it be used with an electrical appliance of rating 5 kW, 200 V?

Solution: Given

Power, P = 5kW = 5000 W

Voltage, V = 200 V

Safe limit of current, I = P/V

I = 5000/200

I = 25 A

As safe limit of appliance is far greater than fuse rating it can not be used.

Question: 12

An electrical kettle is rated 3 kW, 250 V. Give reason whether this kettle can be used in a circuit which contains a fuse of current rating 13 A.

Solution: Given

Power, P = 3kW = 3000 W

Voltage, V = 250 V

Safe limit of current, I = P/V

I = 3000/250

I = 12 A

As safe limit of appliance is less than fuse rating it can be used.

Question: 13

(a.) What is the purpose of a switch in a circuit?

(b.) Why is the switch put in the live wire?

(c.) What precaution do you take while handling a switch?

Solution:

a.) Switch is used to turn the current in circuit on an off.

b.) As an appliance is connected to high potential point through live wire and neutral wire completes the circuit. Hence switch is put in the live wire as if it is connected to neutral wire appliance will turn off when switch is turned of but the appliance will still be connected to high potential point. So, it is dangerous to connect the switch with neutral wire. Hence, switch is connected to live wire.

c.) The switch should not be touched by the wet hands.

Question: 14

(a) A switch is not touched with wet hands while putting it on or off. Give a reason for your answer.

(b) Name the wire to which a switch is connected.

Solution:

a.) Switch should never touched with wet hand as the water forms conducting layer between the live wire and can cause shock to person touching it.

b.) Switch is connected to live wire.

Question: 15

It is dangerous to connect the switch in the neutral wire. Explain your answer.

Solution: As an appliance is connected to high potential point through live wire and neutral wire completes the circuit. Hence switch is put in the live wire as if it is connected to neutral wire appliance will turn off when switch is turned of but the appliance will still be connected to high potential point. So, it is dangerous to connect the switch with neutral wire. Hence, switch is connected to live wire.

Question: 17

Draw a circuit diagram using the dual control switches to light a staircase electric light and explain its working.

Solution:

Diagram below shows the connection made for dual switch. When the bulb is turned on the from switch one the position the circuit is shown below. When the bulb is turned on the from switch two the position the circuit is shown below. Question: 18

What purpose is served by the terminals of a three-way pin plug? Draw a diagram and name the pins.

Solution: The terminals in a three way plug are as follows, top pin is for earthing, left pin is for live wire and right pin is for neutral wire. Question: 18

The diagram in fig. shows a three-pin plug.

Label the three pins.

(a.) Why is top pin thicker and longer than the other two?

(b.) Why are the pins split at the ends?

Solution: a.) Top pin is pin of the earthing. Earthing I for safety of the appliance and safety of humans. Hence, thicker and longer pin used to make sure the connection of the earthing makes connection first.

b.) Pin is split at the end as the should fit in the socket snuggly.

Question: 19

Draw a labelled diagram of a three-pin socket.

Solution: Question: 21

The diagram in Fig. shows a three-pin socket marked as 1, 2 and 3.

(a.) Identify and write live (L), neutral (N) and earth (E) against the correct number.

(b.) To which part of the appliance is the terminal 1 connected?

(c.) To which wire joined to 2 or 3, is the fuse connected?

Solution:

a.) 1- earth, 2- neutral and 3- live

b.) Terminal 1 is connected to outer case of the metallic appliance.

c.) Wire 3 is connected to the fuse being live wire.

Question: 22

What do you mean by the term local earthing? Explain how it is done.

Solution: The local earthing is done in the house near the kWh meter. For this purpose, a hole nearly 2-3 metre deep is dug in the ground. A copper rod covered by a hollow insulating pipe, is inserted in the hole. A thick copper plate of dimension 50 cm x 50 cm is welded at the lower end the copper rod and it is buried inside the ground. The plate is surrounded by a mixture of charcoal and salt to make a contact between the plate and the earth. To keep the ground damp, water is poured through pipe from time to time. This forms a conduction layer between the plate and the ground. The end of the copper rod is joined to the connection at the kWh meter.

Question: 23

To which wire is the metallic case of an electric appliance connected? Give the reason?

Solution: Metallic case of an electrical appliance is connected to earthing. If the appliance or live wire connection turns faulty the metallic case may acquire current and can cause fatal shock to person touching it. But if the metallic case is earthed properly the excessive current will be go the earthing and chances of fatal shock are minimised,

Question: 24

(a.) The earthing of an electric appliance is useful only if the fuse is in the live wire. Give the reason.

(b.) Name the part of the appliance which is earthed.

Solution:

a.) As an appliance is connected to high potential point through live wire and neutral wire completes the circuit. Hence switch is put in the live wire as if it is connected to neutral wire appliance will turn off when switch is turned off but the appliance will still be connected to high potential point. So, it is dangerous to connect the switch with neutral wire. Hence, switch is connected to live wire. Then only the earthing of the appliance is useful.

b.) Metallic case is the part of appliance which is earhed.

Question: 25

For earthing an electrical appliance, one has to remove the paint from the metal body of the appliance where the electrical contact is made. Explain the reason.

Solution: Paint is an insulator, it resists the conduction. Hence, paint is removed from the point of electrical contact.

Question: 26

What is the colour code for the insulation on (a) live, (b) neutral and (c) earth wire?

Solution:

a.) Brown colour for live wire

b.) Blue colour for neutral wire

c.) Green colour for earthing wire.

Question: 27

Name the colour code of the wire which is connected to (i) metallic body of an appliance, (ii) switch for the appliance.

Solution:

i.) Green colour for the earthing wire

ii.) Red colour for the live wire.

Question: 28

How does the colour code of wires in a cable help in house wiring?

Solution: The colour coding of wires in the circuit of house wiring helps us to connect the switch, fuse, sockets through proper wire.

Question: 29

A power circuit uses a cable having three different wires.

(a.) Name the three wires of the cable.

(b.) Between which of the two wires should the heating element of an electric geyser be connected?

(c.)To which wire should the metal case of the geyser be connected?

(d.)To which wire should the switch and fuse be connected?

Solution:

a.) Three wires in the cable are earthing, neutral and live wire.

b.) Between neutral and live wire.

c.) Earthing wire.

d.) Live wire.

Question: 30

State two circumstances when one may get an electric shock from an electric gadget. What preventive measures must be provided with the gadget to avoid it?

Solution: When a metallic case of an appliance comes in direct contact with live wire and earthing is not done properly. One can get shock from that appliance. Hence, preventive measure is earthing of the appliances should be done properly.

When fuse is made of material with high current rating that the safe limit of an appliance, then the appliance may get excessive current fuse will not melt which can cause damage to appliance and shock. Hence, preventive measure is fuse of correct current rating must be used.

Question: 31

Why is it necessary to have an earth wire installed in a power circuit, but not in a lighting circuit?

Solution: As power circuit carries more energy and bigger appliances the damage and shock caused through it can be enormous hence earthing is installed in a power circuit.

MULTIPLE CHOICE TYPE

Question: 1

The rating of a fuse connected in the lighting circuit is:

(a) 15 A

(b) 5 A

(c) 10 A

(d) Zero

Solution: (b)5 A

Question: 2

A switch must be connected in the:

(a) live wire

(b) neutral wire

(c) earth wire

(d) either earth or neutral wire

Solution: (a) live wire

Updated: March 23, 2023 — 4:40 pm