Class 8 Basic Science Chapter 10 Important Questions Kerala Syllabus Static Electricity

The comprehensive approach in SCERT Class 8 Basic Science Textbook Solutions Chapter 10 Static Electricity Important Questions ensure conceptual clarity.

Static Electricity Extra Questions and Answers Class 8 Basic Science Chapter 10 Kerala Syllabus

Static Electricity Class 8 Important Questions

Question 1.
Which of the following devices is used to detect the presence of an electric charge?
a) Capacitor
b) Electroscope
c) Lightning Arrester
d) Voltmeter
Answer:
b) Electroscope

Question 2.
The safe transfer of charge from an object to the Earth is called:
a) Conduction
b) Induction
c) Earthing
d) Repulsion
Answer:
c) Earthing

Question 3.
When a glass rod is rubbed with silk, the glass rod becomes positively charged. This is because:
a) It gains protons
b) It gains electrons
c) It loses protons
d) It loses electrons
Answer:
(d) It loses electrons

Question 4.
Statement 1: Like charges attract each other, and unlike charges repel each other.
Statement 2: Repulsion is the surest test for electrification (charging).
a) Both statements are correct.
b) Only Statement 1 is correct.
c) Only Statement 2 is correct.
d) Both statements are incorrect.
Answer:
c) Only Statement 2 is correct.

Question 5.
Statement 1: A lightning conductor protects a building by providing a safe path for the lightning’s charge to flow to the Earth.
Statement 2: The top of a lightning conductor is made sharp because charges accumulate and discharge more easily from sharp points.
a) Both statements are correct.
b) Only Statement 1 is correct.
c) Only Statement 2 is correct.
d) Both statements are incorrect.
Answer:
a) Both statements are correct.

Question 6.
Statement 1: In charging by conduction, the object being charged gets the same charge as the charging object.
Statement 2: In charging by induction, the object being charged gets the same charge as the charging object.
a) Both statements are correct.
b) Only Statement 1 is correct.
c) Only Statement 2 is correct.
d) Both statements are incorrect.
Answer:
b) Only Statement 1 is correct. (Statement 2 is incorrect; induction gives the opposite charge).

Question 7.
Classify the following materials into Conductors and Insulators:
(Copper, Plastic, Rubber, Silver, Dry Air, Glass, Iron)
Answer:
Conductors: Copper, Silver, Iron
Insulators: Plastic, Rubber, Dry Air, Glass

Question 8.
Categorize the following phenomena as examples of Attraction or Repulsion:
a) A positively charged rod brought near a negatively charged rod.
b) Two balloons rubbed with the same piece of wool brought near each other.
c) A charged balloon sticking to a neutral wall.
d) The leaves of a charged electro scope moving apart.
Answer:
a) Attraction
b) Repulsion
c) Attraction
d) Repulsion

Question 9.
Complete the table related to charging methods:

Method	Physical Contact? (Yes/No)	Charge Gained (Same/Opposite)
Conduction	……….(a)……..	………(b)………
Induction	………(c)………	………(d)………

Answer:
a) Yes
b) Same
c) No
d) Opposite

Question 10.
A student wrote down the following statements. Find the incorrect one(s) and correct them.
a) An atom is neutral because it has no charge.
b) A negatively charged object has an excess of electrons.
c) Protons are transferred when charging by friction.
Answer:
a) Incorrect. Correction: An atom is neutral because it has an equal number of positive protons and negative electrons.

c) Incorrect. Correction: Electrons are transferred when charging by friction.

Question 11.
Find and correct the error in this statement about earthing:
“When a positively charged object is earthed, the positive charges (protons) flow from the object into the Earth.”
Answer:
Error: Protons do not flow.
Correction: When a positively charged object is earthed, electrons flow from the Earth into the object to neutralize it.

Question 12.
A student’s notes on an electroscope are given. Find the mistake and correct it.
“An electroscope is a device used to store electric charge. Its ability to store charge is called capacitance.”
Answer:
Error: This is the definition of a capacitor.
Correction: An electroscope is a device used to detect the presence of electric charge.

Question 13.
A plastic comb rubbed on dry hair can attract small pieces of paper. Why does this happen?
Answer:
When the comb is rubbed on hair, friction causes electrons to transfer from the hair to the comb. The comb becomes negatively charged. This charged comb then attracts the neutral pieces of paper through electrostatic induction (by polarizing the charges in the paper).

Question 14.
Why is it more dangerous to stand under a tall, isolated tree during a thunderstorm?
Answer:
During a thunderstorm, a charged cloud passes overhead. It induces an opposite charge on the ground below. Since a tall tree is the closest point to the cloud and charge accumulates at points, it becomes a prime target for a lightning strike. The lightning will take the easiest path to the ground, which is through the tree.

Question 15.
Why do technicians repairing mobile phones or computers often wear anti-static wrist straps or gloves?
Answer:
The human body can easily build up a static charge. The components inside a mobile phone or computer are extremely sensitive. If a technician touches these components, a static discharge (a tiny spark) can occur, permanently damaging the electronic circuits. The anti-static gear safely earths the technician, preventing any charge from building up.

Question 16.
An atom of Sodium (Na) has 11 protons and 11 electrons.
a) What is the total charge of the atom?
b) If this atom loses one electron, what will be its new charge?
Answer:
a) The total charge is zero (0), or neutral, because the 11 positive protons cancel out the 11 negative electrons.

b) It will have 11 protons (+11) and 10 electrons (-10). The new charge will be +1 (positively charged).

Question 17.
A metal sphere (A) has a charge of -12 units. An identical metal sphere (B) has a charge of +4 units. If the two spheres are touched together and then separated, what will be the final charge on each sphere? Answer:
Total Charge: (-12) + (+4) = -8 units.
When touched, this total charge is shared equally.
Final Charge on Each: -8 / 2 = -4 on sphere A and -4 units on sphere B.

Question 18.
An atom of Chlorine (Cl) has 17 protons.
a) How many electrons does a neutral Chlorine atom have?
b) If this atom gains one electron, what will its charge be?
Answer:
a) A neutral atom must have an equal number of electrons and protons, so it has 17 electrons.
b) It will have 17 protons (+17) and 18 electrons (-18). The new charge will be -1 (negatively charged).

Question 19.
You are given a metal sphere on an insulating stand. Describe the steps to give this sphere a permanent positive charge using the method of induction.
Answer:

1. Step 1: Bring a negatively charged rod (e.g., an ebonite rod rubbed with wool) near the metal sphere, without touching it.
2. Step 2: The free electrons in the sphere are repelled by the rod and move to the far side of the sphere. The side near the rod becomes positively charged.
3. Step 3: While the negative rod is still held nearby, touch the far side of the sphere with your finger. This earths the sphere.
4. Step 4: The repelled electrons now have a path to escape and will flow from the sphere, through your body, and into the Earth.
5. Step 5: Remove your finger first (breaking the earth connection).
6. Step 6: Finally, remove the negative rod. The sphere is now left with a deficit of electrons, giving it a permanent positive charge that spreads evenly over its surface.

Question 20.
You are given a charged rod, but you don’t know if it is positive ‘or’ negative. Describe how you could use an electroscope to find out the sign of the charge.
Answer:

1. Step 1: First, charge the electroscope with a known charge. For example, touch it with a glass rod rubbed with silk. The electroscope is now positively charged, and its leaves will be diverged.
2. Step 2: Bring the unknown charged rod near (do not touch) the metal disc at the top of the charged electroscope.
3. Step 3: (Observe): If the leaves diverge (move further apart): The unknown rod has the same charge as the electroscope. It is positive. (It repels more positive charges down to the leaves).
   If the leaves converge (move closer together): The unknown rod has the opposite charge. It is negative. (It attracts the positive charges from the leaves up towards the disc).

Question 21.
Describe the steps to charge a metal sphere using charging by conduction to give it a negative charge.
Answer:

1. Step 1: Obtain an object that is negatively charged, (e.g., a plastic pen rubbed on dry hair or an ebonite rod rubbed with wool).
2. Step 2: Bring this negatively charged object and touch it directly to the neutral metal sphere.
3. Step 3: When they touch, some of the excess electrons from the charged object will flow onto the neutral sphere, sharing the charge.
4. Step 4: Remove the charging object. The sphere now has an excess of electrons and is permanently negatively charged.

Question 22.
Complete the table

Objects	Electron exchange	Positive	Negative
Glass, silk	From glass rod to silk	………..a………..	Silk
Ebonite, wool	Wool to ebonite	………..b………..	………..c………..
Rubber rod, wool	………..d………..	Wool	………..e………..

Answer:
a. Glass
b. Wool
c. Ebonite
d. From wool to rubber rod
e. Rubber rod

Question 23.
When a glass rod is rub with silk electron loses from the glass rod. If we bring another glass rod near to it what can be observed? Give reason
Answer:
They will repel. Same charges repel each other.

Question 24.
Tick the correct one
1. Object with same charge attract/repel
2. The charged body attract/repel the neutral body
3. bodies with different charges attract/repel.
Answer:
1. repel
2. attract
3. attract

Question 25.
What is the use of capacitor?
Answer:
To store the charge

Question 26.
What is earthing?
Answer:
Connecting an object to earth with a conductor is called earthing.

Question 27.
Examine the following figures and mark the point which charge is accumulated.

Answer:

Question 28.
Complete the figure.

Answer:

Question 29.
Why does the pointed edged conductors are used as lightning conductor
Answer:
The charge accumulated at the pointed edge easily and discharge it to earth immediately. So the building is not effected by lightning

Question 30.
What are the precautions to be taken when lightning
Answer:

• Do not operate electrical equipments
• Do not lay on the wall of the house.
• Do not stand holding windows bar or grill
• Do not stand beneath tall trees
• Do not take shelter under isolated trees

Question 31.
What are the primary steps to be adopted when a person is struck by lightning
Answer:
A person struck by lightning should be made to lie in a place where there is good air circulation. In order to prevent blood clotting keep the body warm by massaging. Give artificial respiration and press strongly on the chest to maintain heart beat and the person must be taken to a hospital immediately

Question 32.
What is dielectric
Answer:
The dielectric are the insulators used in between the plates of the capacitor to increase its capacity Eg. Plastic, polyester, air, paper

Question 33.
What is capacitance. What is its unit
Answer:
capacitance is the ability to store the charge in it. Its unit is fared(F).
1 F = 10⁶ μF(microfared)
1 F = 10¹² pF (picofarad)

Question 34.
You might have seen iron chains, suspended from the body of lorries and trucks touching the earth. What is this for?
Answer:
These lorries and trucks have to travel a long distance. Sometimes the friction between rod and tyre or vehicle and oil in it produces static electricity. This discharge gathers at one end of the truck and it causes sparking and from it the petrol may catch fire. The iron chains suspended from the body of lorries and trucks provide earthing and help to avoid the hazard.

Question 35.
The installation of lightning conductors is not insisted in may tall modern concrete buildings, now-a-days. How are they protected from lightning?
Answer:
In tall modern buildings, there are plenty of metal rods inside the concrete work, connecting from the top to bottom of the building and to the earth. Electric charge from the lightning clouds, reaching the building, is conducted safely to the earth through these metal rods. So the building are protected from damage due to lightning discharge.

Question 36.
A person takes shelter under a tree during heavy rain. Another person shelters under a coconut tree of same height. Who will be safer during lightning? Why?
Answer:
The person standing under the tree is more safe. Electric charge always get concentrated at sharp edges. So more possibility for danger due to lightning is to the man under coconut tree than the other one.

Question 37.
There are two houses nearby, both of them having T.V. antenna pipes. One of these pipes is earthed. Write down the advantages or disadvantages of earthing the pipe.
Answer:
Advantage
When lightning strikes the antenna it does not affect the house if the antenna pipe is earthed. The electric charge of the lightning goes to the earth through the pipe and so it acts as a lightning conductor.

Question 38.
An ebonite rod is rubbed against a piece of wool.
a. What is the electric charge gained by the ebonite rod?
b. If the charged ebonite rod is earthed, electron transfer will be from.
i) ebonite rod to the earth.
ii) the earth to ebonite rod.
Answer:
a. Negative charge
b. i OR ebonite rod to earth.

Question 39.
Observe the picture.

a. Identify the device.
b. Write its use.
c. If a negatively charged object is brought near the metal sphere of the device, what will be the charge acquired on.
i) the metal sphere?
ii) the metal leaves?
Answer:
a. Electroscope
b. To identify and understand the nature of electric charge.
c. (i) Positive (ii) Negative

Question 40.
What happens when two objects carrying a like charge are brought near each other?
a) They attract.
b) They repel.
c) They become neutral.
d) No interaction occurs.
Answer:
b) They repel.

Question 41.
An object that gains electrons through friction acquires what type of charge?
a) Positive charge
b) Negative charge
c) Neutral charge
d) Variable charge
Answer:
b) Negative charge

Question 42.
Which of the following methods is used to charge a conductor with the opposite charge without touching it?
a) Charging by Conduction
b) Charging by Friction
c) Charging by Induction
d) Charging by Direct Contact
Answer:
c) Charging by Induction

Question 43.
Why can a plastic pen be charged by rubbing, but a steel spoon cannot (when held by hand)?
a) Steel is an insulator,
b) Plastic is a better conductor than steel.
c) Steel is a conductor, and the charge flows away through the hand.
d) Plastic has a smaller surface area.
Answer:
c) Steel is a conductor, and the charge flows away through the hand.

Question 44.
What is the primary function of Earthing a charged object?
a) To increase the charge on the object.
b) To provide a safe path for charge to flow to or from the Earth, thereby neutralizing the object.
c) To convert static electricity into current electricity.
d) To store the charge permanently.
Answer:
b) To provide a safe path for charge to flow to or from the Earth, thereby neutralizing the object.

Question 45.
In the context of the Electrostatic Spray Painting application:
a) What charge is given to the paint droplets?
b) Why does the paint stick to the vehicle body?
Answer:
a) Negative charge (-).

b)The paint droplets are negatively charged, and the vehicle body is positively charged. Unlike charges attract, causing the paint to stick strongly and evenly to the surface.

Question 46.
Explain why a gold-leaf Electroscope is a better device for detecting the presence of an electric charge than simply trying to observe attraction to a neutral object.
Answer:
Repulsion is the surest test for electric charge.

• If an object attracts another object, the second object might be charged (opposite charge) or it might be neutral.
• If the leaves of an electroscope repel (diverge), it confirms that the incoming object has successfully charged the leaves (like charge), proving it is charged.

Question 47.
An aluminum sphere is positively charged. Explain briefly how it gets neutralized when it is connected to the Earth (earthed).
Answer:
A positively charged object has a deficiency of electrons. When earthed:

• Electrons flow from the Earth to the object.
• These electrons fill the deficit, and the object’s charge becomes neutral.

Question 48.
Explain the purpose of using a Lightning Conductor on a tall building. Describe itstwo main functions when a charged cloud passes over.
Answer:
Purpose: To protect the building from structural damage, fire, and explosions caused by a massive lightning strike.

• Function 1 (Charge Neutralization): The sharp points induce the opposite charge from the cloud, allowing some gradual discharge to neutralize the cloud’s charge accumulation.
• Function 2 (Safe Path): If lightning strikes, the conductor provides a safe, low-resistance path for the massive electric current to flow directly into the ground, completely bypassing and protecting the building.

Question 49.
A positively charged glass rod is used to charge a neutral metal sphere by induction. Describe the three essential steps required to leave the sphere with a permanent negative charge.
Answer:
Target: Permanent Negative charge using a Positively charged rod.

1. Induction: Bring the positively charged rod near the neutral sphere. (Positive rod attracts electrons to the near side and repels positive charge to the far side).
2. Earthing: While the rod is held in place, connect the sphere to the ground. (Repelled positive charge is neutralized as electrons flow up from the Earth).
3. Isolation & Removal: Remove the earthing connection first, and then remove the rod. (The excess electrons are trapped and redistribute, leaving the sphere permanently negatively charged).

Question 50.
Why are the nozzles used for filling petrol at petrol pumps mandatorily earthed?
Explain the concept of static electricity involved.
Answer:
Concept: The process involves protecting against Electrostatic Discharge (ESD).

Static Build-up: The rapid flow of petrol through pipes and the nozzle creates friction, generating a large static electric charge on the equipment.

Danger: Petrol fumes are highly flammable. If the static charge built up is suddenly discharged (a spark) to the vehicle or ground, it will ignite the fumes, causing a fire or explosion.

Earthing Solution: The earthing connection provides a safe path for any accumulated static charge to continuously flow away into the Earth, ensuring no dangerous sparks can occur during filling.