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)

Short/Long Answer (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.
Answer. False.

(b) Flow of protons constitutes electric current.
Answer. False.

Answer. False.

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

(e) Overloading of electric current in circuits can lead to short circuiting.
Answer. True.

(f) Our body can pass electricity through it.
Answer. True.

(g) All metals are insulators of electricity.
Answer. False.

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

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

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

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

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

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

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

Answer

an insulating material

 (b) Electric work done per unit time is

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

Answer

electrical power

(c) One kilowatt ¡s equal to

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

Answer

1000 watt

 (d) Fuse wire is an alloy of

1.  tin-lead
2.  copper-lead
3.  tin-copper
4.  lead-silver

Answer

tin-lead

(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

Answer

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

Answer

 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.

Answer

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.

Answer

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?

Question-2 :-

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 :-

Question-6 :-

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

Answer-6 :-

The reading is 2 7 8 9

Question-7 :-

Final reading 7657 units
Initial reading 7643 units
Consumption of electricity in a day
=Final reading-initial reading
= 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.

Answer-8 :-

(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)

UNIT in which the electricity bill is charged is board of TRADE
UNIT = kWh
1 Unit = kWh=3600000 J = 3.6 × 10⁶ J
1 kWh= 3.6 × 10⁶ J

Question-10 :-

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

Question-11 :-

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 :-

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

Question-13 :-

Question-19 :-

Fuse is connected with LIVE WIRE.

Question-20 :-

What do you mean by short-circuiting of a circuit?

Answer-20 :-

SHORT CIRCUIT: If the insulation on the cable used in the wiring (or used with an appliance) breaks, THE LIVE WIRE COMES IN CONTACT WITH THE NEUTRAL WIRE, This results in a SHORT CIRCUIT.

Question-21 :-

Figure shows two ways of connecting the three bulbs A, B and C to a battery. Name the two arrangements. Which of them do you prefer to use in a household circuit? Give a reason to support your answer.

Answer-21 :-

Figure (a) is a series arrangement.

Figure (b) is a parallel arrangement. This is preferred because if one bulb gets fused, the other two are still glowing.

Question-22 :-

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, 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-24 :-

State the voltage at which electricity is supplied to our houses.

Answer-24 :-

Electricity voltage is supplied to our houses at 220 volts in India and 120 volts in the USA

Question-25 :- (Electricity ICSE Class-8th Concise)

Draw a labelled diagram with the necessary switches to connect a bulb, a fan and a plug socket in a room with the mains. In what arrangement will you connect them to the mains?

Answer-25 :-

Question-26 :-

State the colour coding of the three wires in a cable used wiring in a household electrical circuit.

Answer-26 :-

Question-27 :-

Why is the metal covering of an electrical appliance earthed?

Answer-27 :-

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?

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)

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.

Answer-4 :-

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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