# Electricity ICSE Class-8th Concise Selina Physics Solutions Ch-8

Electricity ICSE Class-8th Concise Selina Physics Solutions Chapter-8. We Provide Step by Step Answer of Objective, True False , Fill in the blanks,Match the following  Type, Short/ Long Answer and Numerical of Exercise-8 Electricity . Visit official Website  CISCE  for detail information about ICSE Board Class-8.

## Electricity ICSE Class-8th Concise Selina Physics Solutions Part-A

-: Select Topic :-

Objective Questions (A)

Numericals Questions (A)

Electricity Part-B

### A. Objective Questions Sound ICSE Class-8th Concise Selina Part-A

1. Write true or false for each statement:

(a) A fuse wire has a high melting point.

(b) Flow of protons constitutes electric current.

(c) Silver is an insulator of electricity.

(d) S.I. unit and commercial unit of electrical energy are same.

(f) Our body can pass electricity through it.

(g) All metals are insulators of electricity.

(h) The earth wire protects us from an electric shock.

(i) A switch should not be touched with wet hands.

(j) AH electrical appliances in a household circuit work at the same voltage.

(k) In a cable, the green wire is the live wire.

(l) A fuse is connected to the live wire.

(m) A switch is connected to the neutral wire.

2. Fill in the blanks

(a) The unit in which we pay the cost of electricity is kWh.
(b) The electrical energy consumed in a house is measured by kWh meter.
(c) In a household electrical circuit, the appliance are connected in parallel with the mains.
(d) A switch is connected to the live wire.
(e) The red colour insulated wire in a cable is the live wire.
(f) One kilowatt hour is equal to 3.6 x 106 joule.
(g) A fuse wire should have low melting point.

3. Match the following

4. Select the correct alternative

(a) All wires used in electric circuits should be covered with

1.  colouring material
2.  conducting material
3.  an insulating material
4.  none of the above

an insulating material

(b) Electric work done per unit time is

1.  electrical energy
2.  electric current
3.  electric voltage
4.  electrical power

electrical power

(c) One kilowatt ¡s equal to

1.  100 watt
2.  1000 watt
3.  10 watt
4.  none of these

1000 watt

(d) Fuse wire is an alloy of

3.  tin-copper

(e) A fuse wire should have

1.  a low melting point
2.  high melting point
3.  very high melting point
4.  none of the above

a low melting point

(f) When switch of an electric appliance is put off, it disconnects

1.  the live wire
2.  the neutral wire
3.  earth wire
4.  the live and the neutral wire

the live wire

(g) The purpose of an electric meter in a house is

1.  to give the cost of electricity directly
2. give the consumption of electrical energy
3.  to safeguard the circuit from short circuiting
4.  to put on or off the mains.

to give the consumption of electrical energy

(h) If out of the two lighted bulbs in a room, one bulb suddenly fuses, then

1.  other bulb will glow more
2. While other bulb will glow less
3.  other bulb will also fuse
4.  other bulb will remain lighted unaffected.

other bulb will remain lighted unaffected.

### Short/ Long Answer Question Part-A

Selina Concise Physics for ICSE Class-8 Chapter-8 Electricity Solutions

Page-151

#### Question-1 :-

From where does the electricity come to our home?

In our homes, city substation of electricity provides the electricity.

#### Question-2 :-

What is an electric meter? Where is it fixed in our house?

ELECTRIC METER: Is ENERGY meter or kWh meter and measures the amount of electric energy consumed in kWh for which electricity bill is paid.
It is connected through a cable after company fuse on the front or outside wall of the house.

#### Question-3 :-

State the purpose of kWh meter.

Purpose of kWh meter is to measure the electric energy consumed in kWh for which the electricity bill is to be paid. i.e. units of energy consumed.

#### Question-6 :-

The diagram below in the figure shows the reading on the dials of a meter. State what is its reading.

The reading is 2 7 8 9

#### Question-7 :-

One day the meter reading is found to be 7643 units while the next day, it was 7657 units. What is the consumption of electricity in a day?

Consumption of electricity in a day
= 7657 – 7643
= 14 units.

#### Question-8 :-

A source of potential difference V volt sends current I ampere in a circuit for time t second. Write expressions for

1. electrical energy supplied by the source and
2. electrical power spent by the source.

(a) Potential difference is the work done in moving a unit charge

Work done in moving a charge Q through V is

W = QV

But Q/t = I

Or Q = It

W = VIt

As, Work done = Electrical energy

Therefore, Electrical energy = VIt

(b) Power is the rate of doing W

P=W/t=VIt/t = VI

P = VI is the expression.

(Page-152)

#### Question-9 :- (Electricity ICSE Class-8th Concise)

Name the unit in which you pay the cost of your electricity bill. How is it related to joule?

UNIT in which the electricity bill is charged is board of TRADE
UNIT = kWh
1 Unit = kWh=3600000 J = 3.6 × 10J
1 kWh= 3.6 × 10J

#### Question-10 :-

If an appliance of power P watt is used for time t hour. How much electrical energy is consumed in kWh?

Power P = w/t= Electrical energy / t
.’. Electrical energy = P × t

#### Question-11 :-

What is an electric fuse? State its purpose in the household electrical circuit.

FUSE: “Is a safety device that is used to limit the current in an electric circuit.
PURPOSE OF FUSE IN HOUSEHOLD CIRCUIT: It safeguards the circuit and the appliance connected in the circuit from being damaged if the current in the circuit exceeds the specified value due to voltage fluctuation or short-circuiting.

#### Question-12 :-

State one property of the material of a fuse wire.

Two CHARACTERISTICS OF FUSE WIRE are:
(i) Has LOW MELTING POINT.
(ii) Has HIGH RESISTANCE.

#### Question-13 :-

Name the material of a fuse wire.

The material used in fuse wire is an ALLOY of LEAD (50%) and TIN 50% having low M.P. of 200°C

#### Question-19 :-

With which wire: live or neutral is the fuse wire connected?

Fuse is connected with LIVE WIRE.

#### Question-22 :-

How are the electrical appliances connected in a house circuit: in series or in parallel? Give reason.

Electrical appliances in a house are connected in parallel as :

1. Each appliance gets full voltage as resistance in parallel becomes low.
2. If the fuse of one appliance fails it does not affect the working of other appliances.
3. We can light one bulb without lighting the other bulbs.

#### Question-23 :-

In the household electric circuit, if one bulb is fused in a room, the other bulbs keep glowing. Explain the reason.

In the household electric circuit, the appliances are connected in parallel and each appliance has an independent path for current and works at the same voltage. Hence, if one bulb in a room is fused, the other bulbs keep glowing.

#### Question-27 :-

Why is the metal covering of an electrical appliance earthed?

Electrical appliances are earthed to protect from an electric shock. Due to break of insulation of wire, live wire may come in contact with the body of the appliance and pass the current to the appliance and on being touched a fatal shock can occur. On earthing, the appliance will not come in contact with wire, instead the current will pass through the earth and we remain protected from an electric shock.

### Numericals Question Part-A

Chapter-8 Electricity Selina Concise Physics Solutions for ICSE class-8

(Page-152 )

#### Question-1 :-

An electrical appliance is rated as 60 W – 150 V.
(a) What do you understand by this statement?

(b) How much current will flow through the appliance when in use?

(a) 60 W -150 V power rating of appliance means, “If the appliance is put in the circuit on 15 0 volts, it will consume 60 w electrical power i.e. electric energy consumed by it in 1 sec. is 60 J.

P = w/t

∴ Electrical energy W = P × t
P = 1.5 kW t = 30 minutes = 30/60= 1/2hr
1.5 × 1/2= 0.75 kwh

(b)

1 kWh = 3.6 × 106 J
∴ 75 kWh =0.75 × 3.6 × 106
= 2.700 × 106
= 2.7 × 106 J

#### Question-3 :- (Electricity ICSE Class-8th Concise)

Assuming the electric consumption per day to be 12 kWh and the rate of electricity to be? 6.25 per unit, find how much money is to be paid in a month of 30 days?

Electric energy consumed per day = 12 kWh = 12 units
Electric energy consumed in 30 days = 12 × 30 = 360
Units Cost to be paid in 1 month = 360 × 6.25 = ₹ 2250

#### Question-4 :-

In a premise 5 bulbs each of 100 W, 2 fans each of 60 W, 2 A.Cs each of 1.5 kW is used for 5 h per day. Find:
(a) Total power consumed per day,
(b) Total power consumed in 30 days,
(c) Total electrical energy consumed in 30 days.
(d) the cost of electricity at the rate of ₹ 6.25 per unit.

Power consumed by
5 bulbs = 5 × 100 = 500 W
2 fans = 2 × 60= 120 W
2 A.C = 2 × 1.5 x 1000 = 3000 W
(a) Total power consumed per day = 3620 W
(b) Total power consumed in 30 days = 3620/1000 × 30 = 108.6 kw
(c) Electric energy is used for 5 h per day. The total electrical energy consumed in 30 days.
(d) Cost of electricity = P × t = 108.6 × 5 = 543 kWh
= 543 × 6.25 = ₹ 3393.75

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