Question 1

Which of the following cannot be charged easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woollen cloth.

Accepted Answer

Answer: (b) A copper rod
Explanation: Metals like copper are good conductors of electricity and do not hold charge easily because the electrons can move freely and neutralize any charge buildup. Hence, copper rods cannot be charged easily by friction. Plastic scale, inflated balloon, and woollen cloth are insulators and can be charged by friction. — Friction causes transfer of electrons between two materials. Insulators hold the charge as electrons do not move freely, but conductors like copper allow electrons to move freely, preventing charge buildup.

Question 2

When a glass rod is rubbed with a piece of silk cloth the rod
(a) and the cloth both acquire positive charge.
(b) becomes positively charged while the cloth has a negative charge.
(c) and the cloth both acquire negative charge.
(d) becomes negatively charged while the cloth has a positive charge.

Accepted Answer

Answer: (b) becomes positively charged while the cloth has a negative charge.
Explanation: When a glass rod is rubbed with silk, electrons are transferred from the glass rod to the silk cloth. The glass rod loses electrons and becomes positively charged, while the silk cloth gains electrons and becomes negatively charged. — Friction causes transfer of electrons. Glass loses electrons (positive charge), silk gains electrons (negative charge).

Question 3

Write T against true and F against false in the following statements.
(a) Like charges attract each other (T/F)
(b) A charged glass rod attract a charged plastic straw (T/F)
(c) Lightning conductor cannot protect a building from lightning (T/F)
(d) Earthquakes can be predicted in advance (T/F)

Accepted Answer

(a) False - Like charges repel each other.
(b) False - A charged glass rod and a charged plastic straw usually have like charges and repel each other.
(c) False - Lightning conductors protect buildings by safely conducting lightning current to the ground.
(d) False - Earthquakes cannot be predicted in advance with certainty. — Like charges repel, opposites attract. Lightning conductors provide a safe path for lightning. Earthquake prediction is not yet reliable.

Question 4

Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.

Accepted Answer

When you take off a sweater, friction between the sweater and your body causes transfer of electrons, charging the sweater and your body with opposite charges. The crackling sound is due to sudden discharge of static electricity as electrons jump to neutralize the charge difference. — Friction causes static charge buildup; sudden discharge produces crackling sound.

Question 5

Explain why a charged body loses its charge if we touch it with our hand.

Accepted Answer

When a charged body is touched by a hand, the excess charge flows from the body to the earth through the body because the earth acts as a huge reservoir of charge. This neutralizes the charge on the body, causing it to lose its charge. — Human body provides a path for charge to flow to earth, neutralizing the charged body.

Question 6

Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?

Accepted Answer

The scale is the Richter scale.
An earthquake measuring 3 on the Richter scale is a minor earthquake and would be recorded by a seismograph.
It is unlikely to cause much damage as it is a low magnitude earthquake. — Richter scale measures earthquake magnitude. Magnitude 3 is minor, detectable by seismograph but causes little damage.

Question 7

Suggest three measures to protect ourselves from lightning.

Accepted Answer

Three measures to protect ourselves from lightning are:
1. Stay indoors and avoid open fields during thunderstorms.
2. Avoid touching metal objects and electrical appliances.
3. Use lightning conductors on buildings to safely direct lightning to the ground. — Avoiding exposure and using safety devices reduces risk of lightning injury.

Question 8

Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?

Accepted Answer

Two charged balloons have like charges and hence repel each other due to electrostatic repulsion.
An uncharged balloon is attracted by a charged balloon because the charged balloon induces opposite charges on the uncharged balloon, causing attraction. — Like charges repel; induced opposite charges cause attraction.

Question 9

Describe with the help of a diagram an instrument which can be used to detect a charged body.

Accepted Answer

An electroscope is an instrument used to detect a charged body. It consists of a metal rod with thin metal leaves (usually gold or aluminium) at the bottom enclosed in a glass case. When a charged body is brought near the metal cap, the leaves acquire like charges and repel each other, indicating the presence of charge.

[Diagram: Fig. 12.15 or similar electroscope diagram showing metal rod, leaves, glass case] — Charged body induces charge on leaves causing them to repel, showing presence of charge.

Question 10

List three states in India where earthquakes are more likely to strike.

Accepted Answer

Three states in India where earthquakes are more likely to strike are:
1. Jammu and Kashmir
2. Himachal Pradesh
3. Uttarakhand
These states lie in the Himalayan region which is seismically active. — Himalayan states are prone to earthquakes due to tectonic activity.

Question 11

Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?

Accepted Answer

If an earthquake strikes while you are outside, you should:
- Move to an open area away from buildings, trees, streetlights, and power lines.
- Drop to the ground and cover your head and neck.
- Stay there until shaking stops and it is safe to move. — Open areas reduce risk of injury from falling objects during earthquake.

Question 12

The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.

Accepted Answer

It is not advisable to carry an umbrella during a thunderstorm because the umbrella's metal parts can attract lightning, increasing the risk of being struck. Instead, seek shelter indoors or use non-metallic rain gear. — Metal conducts electricity and can attract lightning; safety requires avoiding metal objects during thunderstorms.

Question 13

Open a water tap. Adjust the flow so that it forms a thin stream. Charge a refill. Bring it near the water stream. Observe what happens. Write a short report on the activity.

Accepted Answer

When a charged refill is brought near a thin stream of water, the water stream bends towards the charged refill. This happens because water molecules are polar and get attracted towards the charged object due to electrostatic forces. — Polar water molecules are attracted by the electric field of the charged refill, causing the stream to bend.

Question 14

Make your own charge detector. Take a paper strip roughly 10cm × 3cm. Give it a shape as shown in Fig. 12.15. Balance it on a needle. Bring a charged body near it. Observe what happens. Write a brief report, explaining its working.

Accepted Answer

When a charged body is brought near the paper strip balanced on a needle, the strip moves or is attracted/repelled depending on the charge. This happens because the paper strip gets charged by induction and experiences electrostatic forces. This simple device acts as a charge detector. — The paper strip responds to the electric field of the charged body, indicating presence of charge.

Question 15

This activity should be performed at night. Go to a room where there is a fluorescent tube light. Charge a balloon. Switch off the tube light so that the room is completely dark. Bring the charged balloon near the tubelight. You should see a faint glow. Move the balloon along the length of the tube and observe how the glow changes.

Caution: Do not touch the metal parts of the tube or the wires connecting the tube with the mains.

Accepted Answer

When the charged balloon is brought near the fluorescent tube in a dark room, a faint glow appears due to the electric field of the charged balloon exciting the gas inside the tube. Moving the balloon changes the glow intensity as the electric field varies along the tube. — Electric field from charged balloon excites gas atoms causing glow; glow varies with position.

SOME NATURAL PHENOMENA

SOME NATURAL PHENOMENA — Study Notes

Introduction

12.1 Lightning

The Sparks that the Greeks Knew About

Practice Questions — SOME NATURAL PHENOMENA

All 13 Chapters in Science