Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

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Tamilnadu Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Samacheer Kalvi 8th Science Electricity Text Book Exercises

I. Chosse the best answer

Question 1.
When an ebonite rod is rubbed with fur, the charge acquired by the fur is –
(a) negative
(b) positive
(c) partly positive and partly negative
(d) None of these
Answer:
(b) positive
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 2.
The electrification of two different bodies on rubbing is because of the transfer of –
(a) neutrons
(b) protons
(c) electrons
(d) protons and neutrons
Answer:
(c) electrons

Question 3.
Which of the following a simple circuit must have?
(a) Energy Source, Battery, Load
(b) Energy Source, Wire, Load
(c) Energy Source, Wire, Switch
(d) Battery, Wire, Switch
Answer:
(d) Battery, Wire, Switch

Question 4.
An electroscope has been charged by induction with the help of charged glassrod. The charge on the electroscope is –
(a) negative
(b) positive
(c) both positive and negative
(d) None of the above
Answer:
(b) positive

Question 5.
Fuse is –
(a) a switch
(b) a wire with low resistanceFuse is
(c) a wire with high resistance
(d) a protective device for breaking an electric circuit
Answer:
(d) a protective device for breaking an electric circuit

II. Fill in the blanks

  1. ……………. takes place by rubbing objects together.
  2. The body which has not lost electrons becomes …………….
  3. ……………. is a device that protects building from lightning strike.
  4. ……………. has a thin metallic filament that melts and breaks the connection when the circuit is overheated.
  5. Three bulbs are connected end to end from the battery. This connection is called …………….

Answer:

  1. Transfer of electron
  2. positive
  3. Lightning arrestor
  4. Electric fuse
  5. series circuit

III. State True or False. If false, correct the statement

Question 1.
The charge acquired by an ebonite rod rubbed with a piece of flannel is negative.
Answer:
True

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 2.
A charged body induces an opposite charge on an uncharged body when they are brought near.
Answer:
True

Question 3.
Electroscope is a device used to charge a body by induction.
Answer:
True

Question 4.
Water can conduct electricity.
Answer:
True

Question 5.
In parallel circuit, current remains the same in all components.
Answer:
False
Correct statement:
In parallel circuit, voltage remains the same in all components.

IV. Match the following

Question 1.

  1. Two similar charges – acquires a positive charge
  2. Two dissimilar charges – prevents a circuit from overheating
  3. When glass rod is rubbed with silk – repel each other
  4. When ebonite rod is rubbed with fur – attract each other
  5. Fuse – acquires a negative charge

Answer:

  1. Two similar charges – repel each other
  2. Two dissimilar charges – attract each other
  3. When glass rod is rubbed with silk – acquires a positive charge
  4. When ebonite rod is rubbed with fur – acquires a negative charge
  5. Fuse – prevents a circuit from overheating

V. Give reason for tile following.

Question 1.
When a glass rod is rubbed with silk cloth, both get charged.
Answer:
Reason:
When a glass rod is rubbed with a silk cloth the free electrons in the glass rod are transferred to silk cloth. It is because the free electrons in the glass rod are less tightly bound as compared to that in silk cloth. Since the glass rod looses electrons, it has a deficiency of electrons and hence acquires positive charge. But, the silk cloth has excess of electrons. So, it becomes negatively charged.

Question 2.
When a comb is rubbed with dry hair, it attracts small bits of paper.
Answer:
Reason:
Comb rubbed with hair gains electrons from the hair and becomes negatively charged. These electrons are accumulated on the surface of the comb. When a piece of paper is teared into bits, positive and negative charges are present at the edges of the bits. Negative charges in the comb attract positive charges in the bits. So, the paper bits are moving towards the comb.

Question 3.
When you touch the metal disc of an electroscope with a charged glass rod the metal leaves get diverged.
Answer:
Reason:
The leaves of an electroscope diverge because when a glass rod is touched on the metal disc, the charge travels through the metal rod to the leaves. Since, like charge repel, the charge travels till the leaves and then open up as both the leaves have like charges.

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 4.
In an electroscope the connecting rod and the leaves are all metals.
Answer:
Reason:
These are made of metals so that the electrons become free to move.

Question 5.
One should not use an umbrella while crossing an open field during thunderstorm.
Answer:
Reason:

  1. Carrying an umbrella is not advisable during thunderstorm.
  2. As the rod of umbrella and its supporting wires are made up of metals.
  3. Thus during thunderstorm, the conducting object should be avoided.

VI. Choose the correct answer from the following directions.

Question 1.
(a) If both assertion and reason are true and reason is the correct explanation of the assertion.
(b) If both assertion and reason are true and reason is not the correct explanation of assertion.
(c) If the assertion is true, but reason is false.
(d) If the assertion is false but reason is true.

Question 1.
Assertion : People struck by lightning receive a severe electrical shock.
Reason : Lightning carries very high voltage.
Answer:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.

Question 2.
Assertion : It is safer to stand under a tall tree during lightning.
Reason : It will make you the target for lightning.
Answer:
(d) The assertion is false but reason is true

VII. Answer briefly

Question 1.
How charges are produced by friction?
Answer:
Rubbing certain materials with one another can cause the built-up of electrical charges on the surfaces. So charges are produced by friction.
Example:
Combing hair charges are transferred from the hair to comb due to friction.

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 2.
What is Earthing?
Answer:
Earthing is the process of connecting the exposed metal parts of an electrical circuit to the ground.

Question 3.
What is electric circuit?
Answer:
The path through which electrons flow from one terminal to another terminal of the source, is called electric circuit.

Question 4.
What is electroplating?
Answer:
The process of depositing a layer of one metal over the surface of another metal by passing electric current is called electroplating.

Question 5.
Give some uses of electroplating.
Answer:
Electro plating is applied in many fields:

  1. We use iron in bridges and automobiles to provide strength.
  2. A coating of zinc is deposited on iron to protect it from corrosion and formation of rust.
  3. Chromium has a shiny appearance. It does not corrode.
  4. It resists scratches.

VIII. Answer is detail

Question 1.
Explain three ways of charge transfer.
Answer:
Transfer of charges takes place in the following three ways:

  1. Transfer by Friction
  2. Transfer by Conduction
  3. Transfer by Induction

1. Transfer by Friction:
This method of charging an uncharged body by rubbing it ; against another body is called charging by friction.
Example:
While combing hair charges are transferred from the hair to comb due to friction.

2. Transfer by conduction:
Charges can be transferred to on object by bringing it in contact with a charged body. This method of transferring charges from one body to other body is calledtransfer by conduction.
Example:
When the ebonite rod is rubbed with woollen cloth, electrons from the woollen cloth are transferred to the ebonite rod. Now ebonite rod will be negatively charged.

(i) When it is brought near the paper cylinder, negative charges in the rod are attracted by the positive charges in the cylinder.

(ii) When the cylinder is touched by the rod, some negative charges are transferred to the paper. Hence, the negative charges in the rod are repelled by the negative charges in the cylinder.

3. Transfer by Induction:
The process of charging an uncharged body by bringing a charged body near to it but without touching it is called induction.
Example:
we can charge an uncharged object when we touch it by a charged object. But, it is also possible to obtain charges in a body without any contact with other charges.

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 2.
What is electroscope? Explain how it works?
Answer:
1. An electroscope is a scientific instrument used to detect the presence of electric charge on a body.

2. An electroscope is made out of conducting materials, generally metal.

3. It works on the principle that like charges repel each other.

4. In a simple electroscope two metal sheets are hung in contact with each other.

5. They are connected to a metal rod that extends upwards, and ends in a knob at the end.

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 1

6. If you bring a charged object near the knob, electrons will either move out of it or into it.

7. This will result in charges on the metal leaves inside the electroscope.

8. If a negatively charged object is brought near the top knob of the electroscope, it causes free electrons in the electroscope to move down into the leaves, leaving the top positive..

9. Since both the leaves have negative charge, they repel each other and move apart.

10. If a positive object is brought near the top knob of the electroscope, the free electrons in the electroscope start to move up towards the knob.

11. This means that the bottom has a net positive charge. The leaves will spread apart again. Explain series and parallel circuit.

Question 3.
Explain series and parallel circuit.
Answer:
Series Circuit:
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 2

  1. A series circuit is one that has more than one resistor (bulb) but only one path through which the electrons can travel.
  2. From one end of the battery the electrons move along one pathwith no branches through the resistors (bulbs) to the other end of the cell.
  3. All the components in a series circuit are connected end to end.
  4. So, current through the circuit remains same throughout the circuit.
  5. But, the voltage gets divided across the bulbs in the circuit.
  6. In the following series circuit two bulbs are used as resistors.
  7. Let I be the current through the circuit and V1 V2, V3 be the voltage across each bulb.
  8. The supply voltage V is the total of the individual voltage drops across the resistances. V = V1 + V2 + V3

Parallel Circuit:
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 3

  1. In a parallel circuit, there is more than one resistor (bulb) and they are arranged on many paths.
  2. This means charges (electrons) can travel from one end of the cell through many branches to the other end of the cell.
  3. Here, voltage across the resistors (bulbs) remains the same but the current flowing through the circuit gets divided across each resistor.
  4. Let us consider three bulbs connected in series.
  5. Let V be the voltage across the bulbs and I1, I2, I3 be the current across each bulb.
  6. The current I from the battery is the total of the individual current flowing through the resistances. I = I1 + I2 + I3

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 4.
How lightning takes place?
Answer:
1. Lightning is produced by discharge of electricity from cloud to cloud or from cloud to ground.

2. During thunderstorm air is moving upward rapidly.

3. This air which moves rapidly, carries small ice crystals upward.

4. At the same time, small water drops move downward.

5. When they collide, ice crystals become positively charged and move upward and the water drops become negatively charged and move downward.
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 4
6. So the upper part of the cloud is positively charged and the lower part of the cloud is negatively charged.

7. When they come into contact, electrons in the water drops are attracted by the positive charges in the ice crystals. Thus, electricity is generated and lightning is seen.

8. Sometimes the lower part of the cloud which is negatively charged comes into contact with the positive charges accumulated near the mountains, trees and even people on the earth. This discharge produces lot of heat and sparks that results in what we see as lightning.

Question 5.
What is electroplating? Explain how it is done.
Answer:
Electroplating:
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 5

  1. Electroplating is one of the most common applications of chemical effects of electric current.
  2. The process of depositing a layer of one metal over the surface of another metal by passing electric current is called electroplating.
  3. Take a glass jar and fill it with copper sulphate solution.
  4. Take a copper metal plate and connect it to the positive terminal of battery.
  5. Connect an iron spoon to the negative terminal of the battery.
  6. Now, dip them in the copper sulphate solution.
  7. When electric current is passed through the copper sulphate solution, you will find that a thin layer of copper metal is deposited on the iron spoon and an equivalent amount of copper is lost by the copper plate.

Samacheer Kalvi 8th Science Electricity Intex Activities

Activity – 1

Question 1.
Take a comb and place it near some pieces of paper. Are they attracted by the comb? No. Now comb your dry hair and place it near them. What do you see? You can see that the paper pieces are attracted by the comb now. How is it possible?
Answer:
Reason:
Comb rubbed with hair gains electrons from the hair and becomes negatively charged. These electrons are accumulated on the surface of the comb. When a piece of paper is teared into bits, positive and negative charges are present at the edges of the bits. Negative charges in the comb attract positive charges in the bits. So, the paper bits are moving towards the comb.

Activity – 2

Question 1.
Take a sheet of paper. Turn it into a hollow cylinder. Tie one end of the cylinder with a silk thread and hang it from a stand. Now take an ebonite rod and charge it by rubbing it with a woollen cloth. Bring this charged ebonite rod near the paper cylinder. The cylinder will be attracted by the rod. If you touch the paper cylinder by the charged rod, you will see the paper cylinder repelling the rod. Can you give the reason?
Answer:
When the cylinder is touched by the rod, some negative charges are transferred to the paper. Hence, the negative charges in the rod are repelled by the negative charges in the cylinder.

Activity – 4

Question 1.
Rub your foot on a carpet floor and touch a door knob. What do you feel? Do you feel the shock in your hand? Why does this happen?
Answer:
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 6
Getting a shock from a doorknob after rubbing your foot on a carpet floor, results from discharge. Discharge occurs when electrons on the hand are quickly pulled to the positively charged doorknob. This movement of electrons, which is felt as a shock, causes the body to lose negative charge.

Activity – 5

Question 1.
Take two pieces of wire, an LED light and a battery, and make a simple electric circuit. Take some water in a glass and put the wires in the water as shown in the figure. Does the LED bulb glow? What do you understand from this?
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 7
Answer:
Yes, the LED bulb glows. From this Activity we understood that liquids also conduct electricity.

Activity – 7

Question 1.
Take a battery, a bulb, a switch and few connecting wires. Make an electric circuit as shown in the figure. Keep the switch in the ‘OFF’ position. Does the bulb glow?
Answer:
No, the bulb does not glow.
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 8

Question 2.
Now move the electric switch to the ‘ON’ position and let the bulb glow for a minute or so. Touch the bulb now. Do you feel the heat?
Answer:
Yes, the bulb is hot because electrical energy is transformed to heat energy. This is known as heating effect of electric current.

Samacheer Kalvi 8th Science Electricity Additional Questions

I. Choose the correct answer

Question 1.
Electroplating is based on ……………… effect of electricity.
(a) magnetic
(b) chemical
(c) heating
(d) physical
Answer:
(b) chemical

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 2.
A positively charged object will attract ……………… charged object.
(a) positively
(b) negatively
(c) both a and b
(d) none
Answer:
(b) negatively

Question 3.
The method of charging an object by touching is called ………………
(a) induction
(b) diffusion
(c) current
(d) conduction
Answer:
(d) conduction

Question 4.
Lighting occurs due to ……………….
(a) rain
(b) humidity
(c) wind
(d) electric discharge
Answer:
(d) electric discharge

Question 5.
Electric charge can be transferred from a charged object to another through ……………….
(a) vacuum
(b) conductor
(c) air
(d) insulator
Answer:
(b) conductor

Question 6.
Electric charge is measured in ……………….
(a) volt
(b) coulomb
(c) ampere
(d) watt
Answer:
(b) coulomb

Question 7.
The value of charge of an electron is equal to ……………….
(a) 6.04 x 10-19 C
(b) 1.602 x 10-18 C
(c) 1.602 x 10-19 C
(d) 6.10 x 10-18 C
Answer:
(c) 1.602 x 10-19 C

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 8.
Before using electroscope, it should be ………………..
(a) charged
(b) closed
(c) discharged
(d) cleaned
Answer:
(c) discharged

Question 9.
Lighting rods are made of ………………..
(a) copper
(b) plastic
(c) sand paper
(d) wood
Answer:
(a) Copper

Question 10.
Electricity produced on rubbing is ……………….
(a) static electricity
(b) current electricity
(c) electromagnet
(d) none
Answer:
(a) static electricity

Question 11.
The materials which allows electric current to pass through it, is called ……………….
(a) conductor
(b) insulator
(c) both a and b
(d) none of these
Answer:
(a) conductor

Question 12.
The material which does not allow electric current is called ………………..
(a) solution
(b) metal
(c) insulator
(d) electrolyte
Answer:
(c) insulator

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 13.
All metals are ………………..
(a) conductors
(b) insulators
(c) electrolytes
(d) none
Answer:
(a) conductors

Question 14.
An electrolyte ……………….
(a) has positive charge
(b) has negative charge
(c) should be able to conduct charge without dissociating.
(d) should be able to form positive and negative ions.
Answer:
(d) should be able to form positive and negative ions

Question 15.
Most common industrial application of chemical effects of electric current is ………………..
(a) Anodizing
(b) electroplating
(c) electrolysis
(d) none
Answer:
(b) electroplating

Question 16.
The terminal which is connected to a positive terminal of a battery is called ……………….
(a) anode
(b) cathode
(c) neutral
(d) none
Answer:
(a) anode

Question 17.
Flow of per unit time is called current ………………..
(a) charge
(b) proton
(c) neutron
(d) all of these
Answer:
(a) charge

Question 18.
Liquids that conduct electricity are the solutions of ………………..
(a) acids
(b) bases
(c) salts
(d) all of these
Answer:
(d) all of these

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 19.
A tiny particle which rotates around the nucleus of an atom is ………………..
(a) proton
(b) electron
(c) neutron
(d) both a and b
Answer:
(b) electron

Question 20.
……………….. wire is used in the filament of the bulbs.
(a) Nichrome
(b) Copper
(c) Tungsten
(d) None
Answer:
(c) Tungsten

II. Fill in the blanks

  1. Comb rubbed with hair ……………. electrons from the hair and becomes negatively charged.
  2. Electric charge is measured in ……………..
  3. Since, protons and electrons are equal in number, an atom is electrically ………………
  4. When an ebonite rod is rubbed with fur, the fur transfers …………….. to the ebonite rod.
  5. Before the discovery of electrons, it was considered that electric current is due to the flow of …………….. charges.
  6. The gold – leaf electroscope was developed by ………………
  7. …………….. is an example of discharge that takes place in clouds.
  8. During thunderstorm air is moving …………….. rapidly.
  9. Huge quantities of electricity are discharged in light flashes and temperatures of over ……………..°C or more can be reached.
  10. …………….. extreme heat will vaporize the water inside a tree, creating steam that may bum out the tree.
  11. …………….. is a device used to protect buildings from the effects of lightning .
  12. …………….. is a species offish which can give electric shocks.
  13. In series circuit, the current remains …………….. throughout the circuit.
  14. …………….. is used in extraction and purification of metals.
  15. Copper wire offers very little …………….. and does not get heated up quickly.
  16. A fuse is a strip of alloy wire which is made of lead and tin with a very low ………………
  17. The flow of ……………… per unit time is called current.

Answer:

  1. gains
  2. coulomb
  3. neutral
  4. electrons
  5. positive
  6. Abraham Bennet
  7. Lightning
  8. upward
  9. 30,000
  10. Lightning’s
  11. Lightning arrestor
  12. Electric eel
  13. same
  14. Electrolysis
  15. resistance
  16. melting point
  17. charge

III. True or False – if false give the correct statement

Question 1.
Materials which do not allow electric charges to pass through them easily are called insulator.
Answer:
True

Question 2.
Silk cloth has excess of electrons, so it becomes positively charged.
Answer:
False
Correct statement:
Silk cloth has excess of electrons, so it becomes negatively charged.

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 3.
Electric charge is measured in coulomb.
Answer:
True.

Question 4.
Protons carry negative charge and the electrons carry positive charge.
Answer:
False.
Correct statement:
Protons carry positive charge and the electrons carry negative charge.

Question 5.
The gold – leaf electroscope was developed by Abraham Bennet.
Answer:
True

IV. Match the following

Question 1.

1.

Bulb

(a) Conductor
2. Electroplating (b)

Insulator

3.

Pure water (c) Heating effect of current
4. Salt solution (d)

Chemical effect of current

Answer:

  1. c
  2. d
  3. b
  4. a

Question 2.

1.

Insulator (a) Coulomb
2. Conductor (b)

Electric circuit

3.

Closed path (c) Copper
4. Electric charge (d)

Rubber

Answer:

  1. b
  2. c
  3. d
  4. a

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 3.

1.

Anode (a) Conducting solution
2. Cathode (b)

Positive terminal

3.

Ions (c) Negative terminal
4. Electrolyte (d)

Positively or negatively charged

Answer:

  1. d
  2. c
  3. a
  4. b

V. Read the directions given below and answer the questions.

Question 1.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.

Question 1.
Assertion : Charges flow from higher potential to the lower potential.
Reason : Current flows mainly due to flow of electrons.
Answer:
(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion

Question 2.
Assertion : Parts of car and bicycle are made iron with chromium coating.
Reason : Chromium does not corrode and resist scratches.
Answer:
(a) Both assertion and reason are true and the reason is the correct explanation of the assertion

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 3.
Assertion : Insulators do not allow flow of current through them.
Reason : Insulators have no free charge carrier
Answer:
(a) Both assertion and reason are true and the reason is the correct explanation of the assertion

Question 4.
Assertion : A current carrying wire should be charged.
Reason : The current in a wire is due to flow of free electrons in a definite direction.
Answer:
(d) The assertion is false, but the reason is true

Question 5.
Assertion : When both the strips of electroscope is charged with similar charge, they repel each other and become wide open.
Reason : Like charges always repel each other.
Answer:
(a) Both assertion and reason are true and the reason is the correct explanation of the assertion

VI. Answer briefly

Question 1.
Name the process which show the chemical effect of electric current?
Answer:
Electroplating.

Question 2.
What are electrodes?
Answer:
The metal rods dipped in liquids to which cells are attached are called electrodes.

Question 3.
Who discovered static electricity or lightning in clouds?
Answer:
Benjamin Franklin in 1752.

Question 4.
What are charged objects?
Answer:
The objects which acquire a small charge on rubbing are called charged objects.

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 5.
What do you mean by earthing?
Answer:
The process of transferring of charge from a charged object to the earth is called earthing.

Question 6.
A layer of zinc coated over iron. Why?
Answer:
Layer of zinc coated over iron because zinc prevents it from rust and corrosion.

Question 7.
Name the effect of current responsible for the glow of the bulb in an electrical circuit.
Answer:
Heating effect of electric current.

Question 8.
Name a few appliances which work on the basis of heating effect of current.
Answer:
Bulb, iron, heater, electric kettles, electric cookers, electric fuse.

Question 9.
What are the essential components of an electric circuit?
Answer:
Electric cell, bulb, switch, battery and connecting wires.

Question 10.
How can you save yourselves from lightning?
Answer:

  1. We should remain in the covered area.
  2. we should not use wired telephones during lightning.

Question 11.
State some advantages electroplating.
Answer:

  1. It protects the metal from corrosion and rusting.
  2. It is used to coat desired metal on other objects.
  3. It can make more reactive metal like iron.
  4. Coating of chromium on the metal gives luster to the objects.

Question 12.
Write the differences between conductors and insulators.
Answer:
Conductors:
Materials which allow the electric current to pass through them are called conductors.
Example:
All metals, Salt water

Insulators:
Materials do not allow the current to pass through them are called insulators.
Example:
Dry wood, plastics, rubber, glass

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 13.
What are anodes and cathodes?
Answer:

  1. In the process of electrolysis, the electrode which is connected to the positive terminal of the battery is called anode.
  2. The electrode which is connected to the negative terminal of the battery is called cathode.

Question 14.
What will be the charges on silk and glass rod when they are rubbed against each other?
Answer:

  1. When a glass rod is rubbed with silk piece, the free electrons in the glass rod are transferred to silk piece.
  2. It is because the free electrons in the glass rod are tightly bound as compared to that in silk piece.
  3. Since the glass rod looses electrons, it has a deficiency of electrons and hence acquires positive charge.
  4. But, silk piece has excess of electrons.
  5. So, it becomes negatively charged.

Question 15.
When a negatively charged glass rod is brought near another glass rod, the rod will move apart. Give reason.
Answer:
It is because both the glass rods are negatively charged. So they repel each other.

Question 16.
When an ebonite rod is rubbed with fur, the fur transfers electrons to the ebonite rod. Why?
Answer:

  1. It is because the electrons in the outermost orbit of the atoms in fur are loosely bound as compared to the ebonite rod.
  2. Ebonite rod has excess electrons which becomes negatively charged and the fur which has deficiency of electrons is positively charged.

Question 17.
List the ways in which you can charge an object.
Answer:

  1. Charging by friction
  2. Charging by induction
  3. Charging by conduction.

Question 18.
How thunder takes place?
Answer:

  1. Huge, quantities of electricity are discharged in lightning flashes and temperatures of over 30,000°C or more.
  2. This extreme heat causes the air to expand explosively fast and then they contract.
  3. This expansion and contraction create a shock wave that turns into a booming sound wave known as thunder.

Question 19.
Sometimes lighting may be seen before the thunder is heard. Why?
Answer:
It is because the distance between the clouds and the surface is very long and the speed of light is much faster than the speed of sound.

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 20.
What do you mean by electrical Earthing?
Answer:
Electrical Earthing is defined as the process of transferring the discharge of electrical energy directly to the Earth With the help of low-resistance wire.

VII. Answer in detail

Question 1.
Explain the structure and working of gold-leaf electroscope with a diagram.
Answer:
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 9
Structure of I metroscope :

  1. It is made up of a glass jar.
  2. A vertical brass rod is inserted into the jar through a cork.
  3. The top of the brass rod has a horizontal brass rod or a brass disc.
  4. Two gold leaves are suspended from the brass rod inside the jar.

Working of Electroscope:

  1. When the brass disc of the electroscope is touched by a charged object, electric charge
  2. gets transferred to the gold leaf through the rod.
  3. This results in the gold leaves moving away from each other.
  4. This happens because both the leaves have similar charges.

Question 2.
Write a note on –

  1. Charging
  2. Electrical discharge.

Answer:
1. Charging:
Transfer of charge from one object to another is called charging. In case of the gold leaves charge is transferred through the brass rods.

2. Electrical Discharge:
The gold leaves resume their normal position after some time. This happens because they lose their charge. This process is called electrical discharge. The gold leaves would also be discharged when someone touches the brass rod with bare hands. In that case, the charge is transferred to the earth through the human body.

Question 3.
Explain the function of lightning arrestor with a diagram.
Answer:
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 10

  1. Lightning arrestor is a device used to protect buildings from the effects of lightning.
  2. Lightning conductor consists of a metallic lightning rod that remains in air at the top of the building.
  3. Major portion of the metal rod and copper cable are installed in the walls during its construction.
  4. The other end of the rod is placed deep into the soil.
  5. When lightning falls, it is attracted by the metallic rods at the top of the building.
  6. The rod provides easy route for the transfer of electric charge to the ground.
  7. In the absence of lightning arrestors, lightning will fall on the building and the building will be damaged.

Question 4.
Write a note on.

  1. Fuse
  2. Electric irons.

Answer:
1. Fuse:

  1. Fuse is a strip of alloy wire which is made up of lead and tin with a very low melting point.
  2. This can be connected to the circuit.
  3. The fuse is usually designed to take specific amount of current.
  4. When current passing through the wire exceeds the maximum limit, it gets heated up.
  5. Due to low melting point, it melts quickly disconnecting the circuit. This prevents damage to the appliances.

2. Electric irons :

  1. When current flows through the heating element, the heat energy developed is conducted to the heavy metal base, raising its temperature.
  2. This energy is then used to press clothes.

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 5.
Distinguish between series and parallel circuit.
Answer:
Series circuit:

  1. Same amount of current flows through all the components.
  2. Voltage is different across different components.
  3. Components are arranged in a line.
  4. If one component breaks down, the whole circuit will bum out.

Parallel circuit:

  1. The current flowing through each component combines to form the current flow.
  2. Sum of the voltage through each component will be the voltage drawn from the source.
  3. Components are arranged parallel to each other.
  4. Other components will function even if one component breaks down.

VIII. Picture based Questions

Question 1.
Will the bulb glow if the end B is dipped in pure water?
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 11
Answer:
No, the bulb will not glow as pure water is an insulator.

Question 2.
Identify the charge on the body with a question mark.
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 12
Answer:
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 13

Question 3.
The bulb does not glow in the set up show in figure. List the possible reasons.
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 14
Answer:
The possible reasons are:

  1. Bulb may be fused.
  2. Cells may be used up.
  3. The liquid may be poor conductor of electricity.
  4. The connection of the circuits may be loose.

IX. Higher Order thinking skills (HOTS):

Question 1.
During the construction of a building, the lightning conductor was left hanging in the air by mistake will it be effective? Explain.
Answer:
Lighting conductor will not work. It left hanging in the air because in order to work, it must be installed properly and grounded using copper plate.

Question 2.
During lightning and thunder we should avoid standing in ground and open spaces Why?
Answer:
During lightning and thunder, we should avoid standing in ground and open spaces. You should make yourself as small as possible by squating. It is however safe to stay inside a car because the car acts as a shield and protects us from the electric field generated by the storm.

Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity

Question 3.
You might have observed on a dry day that when you touch the screen of a television you get a slight shock. Why does it happen?
Answer:
It happens because the television screen is charged and have static charges and when we touch with our hands which are uncharged, the charges attract our hands and transfer through our hands and we get a small shock.

X. Solve the following crossword with the help of the given clues.

Clue:
Across :
1. Ions having a positive charge formed by the loss of electrons.
2. Chemical compound which conducts electricity when in aqueous state.
5. Atoms that have an electric charge.
7. A piece of metal through which an electric current enters or leaves in a liquid or gas.

Down :
3. A process in which a thin film of metal is deposited on another metal with the help of electricity.
4. A process in which a chemical change especially decomposition of a chemical compound is brought about by passing an electric current through a solution.
6. Ions having a negative charge formed by the gain of electrons.
8. The negative electrode is an electrolytic cell, toward which positively charged particles are attracted.
Answer:
Samacheer Kalvi 8th Science Solutions Term 2 Chapter 2 Electricity 15

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