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 :-
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.
(d) S.I. unit and commercial unit of electrical energy are same.
(e) Overloading of electric current in circuits can lead to short circuiting.
(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
- colouring material
- conducting material
- an insulating material
- none of the above
an insulating material
(b) Electric work done per unit time is
- electrical energy
- electric current
- electric voltage
- electrical power
(c) One kilowatt ¡s equal to
- 100 watt
- 1000 watt
- 10 watt
- none of these
(d) Fuse wire is an alloy of
(e) A fuse wire should have
- a low melting point
- high melting point
- very high melting point
- none of the above
a low melting point
(f) When switch of an electric appliance is put off, it disconnects
- the live wire
- the neutral wire
- earth wire
- the live and the neutral wire
the live wire
(g) The purpose of an electric meter in a house is
- to give the cost of electricity directly
- give the consumption of electrical energy
- to safeguard the circuit from short circuiting
- 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
- other bulb will glow more
- While other bulb will glow less
- other bulb will also fuse
- 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
From where does the electricity come to our home?
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.
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-4 :- (Electricity ICSE Class-8th Concise)
For which unit do we pay our electricity bill?
UNIT is a board of trade unit which is kWh (Kilowatt per hour) = 1000 W used in 1 hour.
How can you check just by seeing the meter whether the electricity is in use or not?
(A red mark is seen rotating).
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
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?
Final reading 7657 units
Initial reading 7643 units
Consumption of electricity in a day
=Final reading-initial reading
= 7657 – 7643
= 14 units.
A source of potential difference V volt sends current I ampere in a circuit for time t second. Write expressions for
- electrical energy supplied by the source and
- 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.
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 × 106 J
1 kWh= 3.6 × 106 J
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
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.
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.
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
Can we use copper wire as a fuse wire? Give reason.
Copper wire cannot be used as a fuse wire since the melting point of Copper (Cu) is high and resistance is very low. The current can flow through without melting it which can damage the appliances.
Question-15 :- (Electricity ICSE Class-8th Concise)
How does a fuse protect the electric wiring (or an appliance) from being damaged?
Due to voltage fluctuations or insulation on the wire of cable gets worn and torn (breaks), the live wire comes in contact with the neutral wire and results in SHORT CIRCUIT. To prevent this damage, a fuse is used in the LIVE WIRE. The fuse wire gets heated up to the extent that it melts, a gap is produced in the live wire and the circuit becomes incomplete, no current flows and the appliance is saved.
Which fuse wire is thick: 5 A or 15 A?
More the area, lesser is the resistance and more is the current flowing.
∴ 15 A fuse wire is thick.
Write the full form of M.C.B?
Miniature Circuit Breaker
How is M.C.B. superior to the fuse wire?
MCB is more sensitive to current than a fuse. It detects any abnormality in the current flow and automatically switches off the electrical circuit.
MCB doesn’t need to be replaced every time when high current passes from it but fuse needs to be replaced because it melts and breaks
With which wire: live or neutral is the fuse wire connected?
Fuse is connected with LIVE WIRE.
What do you mean by short-circuiting of a circuit?
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.
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.
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 :
- Each appliance gets full voltage as resistance in parallel becomes low.
- If the fuse of one appliance fails it does not affect the working of other appliances.
- We can light one bulb without lighting the other bulbs.
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.
State the voltage at which electricity is supplied to our houses.
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?
State the colour coding of the three wires in a cable used wiring in a household electrical circuit.
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
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.
∴ Current will through the appliance I= P/V = 60 w/150 v = 0.4 A
An electric iron of power 1.5 kW is used for 30 minutes to press the clothes.
(a) Calculate the electrical energy consumed in kilowatt-hour
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
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
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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