Question 1

What is lightning and how does it occur during a thunderstorm?

Accepted Answer

Lightning is a sudden electrostatic discharge between electrically charged regions within clouds or between clouds and the ground. It occurs when air currents inside thunderclouds cause separation of charges, with positive charges accumulating at the top and negative charges at the bottom, leading to a discharge when the charge difference is large enough. — Lightning is caused by the separation of electric charges inside thunderclouds due to air currents. Positive charges collect at the top and negative charges at the bottom of the cloud. When the difference in charge becomes very large, an electrostatic discharge occurs as lightning. This process heats the air rapidly, causing thunder.

Question 2

Which of the following statements correctly describes the reason why thunder is heard after lightning?

Accepted Answer

Light travels faster than sound, so lightning is seen before thunder is heard. — Lightning is a flash of light which travels at the speed of light, much faster than sound. Thunder is the sound caused by rapid expansion of heated air and travels slower. Hence, we see lightning before hearing thunder.

Question 3

What safety device is used on buildings to protect them from lightning strikes, and how does it work?

Accepted Answer

A lightning conductor or lightning rod is used to protect buildings. It provides a safe path for the electric discharge from lightning to flow into the ground, preventing damage and fires. — Lightning rods are metal rods fixed on top of buildings and connected to the ground. When lightning strikes, the electric charge is safely conducted through the rod to the earth, avoiding damage to the building.

Question 4

Which of the following materials is an insulator?

Accepted Answer

Plastic — Plastic is an insulator because it does not allow electric charges to flow freely. Copper, aluminium, and iron are conductors that allow electric current to pass.

Question 5

When a plastic comb is rubbed on dry hair, it attracts small pieces of paper. What causes this attraction?

Accepted Answer

The comb becomes charged by rubbing, gaining electrons and becoming negatively charged. The charged comb induces opposite charges on the neutral paper pieces, causing attraction between the comb and paper. — Rubbing transfers electrons to the comb, charging it negatively. The neutral paper pieces experience induced charges with positive charges closer to the comb, resulting in attraction due to opposite charges.

Question 6

What are the poles of a magnet and how do they interact with each other?

Accepted Answer

A magnet has two poles called the north (N) pole and the south (S) pole. Like poles repel each other, while unlike poles attract each other. — The north and south poles are the ends of a magnet where magnetic forces are strongest. When two magnets are brought close, similar poles push away (repel), and opposite poles pull together (attract).

Question 7

How does a freely suspended magnet behave and why?

Accepted Answer

A freely suspended magnet aligns itself along the north-south direction because Earth behaves like a giant magnet with a magnetic north and south pole, causing the magnet to align with Earth's magnetic field. — Earth's magnetic field exerts force on the magnet's poles, making it rotate until its north pole points towards Earth's magnetic north and its south pole towards Earth's magnetic south, helping in navigation.

Question 8

Which of the following correctly describes the direction of magnetic field lines around a bar magnet?

Accepted Answer

They emerge from the north pole and enter the south pole. — Magnetic field lines always emerge from the north pole of a magnet and enter the south pole, forming closed loops around the magnet.

Question 9

Explain how an electric current produces a magnetic field around a wire.

Accepted Answer

When electric current flows through a wire, it produces a magnetic field around the wire. This magnetic field can be detected by the deflection of a nearby compass needle. — Electric current creates circular magnetic field lines around the wire. The compass needle placed near the wire aligns with this magnetic field and deflects from its usual north-south alignment, showing the magnetic effect of current.

Question 10

What is an electromagnet and how is it made?

Accepted Answer

An electromagnet is a temporary magnet made by passing electric current through a coil of wire wrapped around an iron core, magnetizing the core as long as current flows. — When current flows through the coil, it produces a magnetic field that magnetizes the iron core, creating a strong magnet. When the current stops, the magnetism disappears, making it temporary.

Question 11

Which of the following is NOT an application of electromagnets?

Accepted Answer

Compass needles — Compass needles are permanent magnets that align with Earth's magnetic field and do not rely on electromagnets. Electric bells, cranes, and magnetic locks commonly use electromagnets.

Question 12

Describe the working of an electric bell with the role of each part.

Accepted Answer

(a) The electric bell consists of a switch, electromagnet, hammer, gong, and spring.
(b) When the switch is pressed, current flows through the electromagnet, magnetizing the iron core.
(c) The electromagnet attracts the hammer which strikes the gong producing sound.
(d) As the hammer moves, the circuit breaks, stopping current and demagnetizing the electromagnet.
(e) The spring pulls the hammer back, completing the circuit again, repeating the cycle and producing ringing sound. — The electric bell converts electrical energy into mechanical energy and sound.
(a) Pressing the switch closes the circuit, allowing current to flow.
(b) The electromagnet becomes magnetized and attracts the hammer.
(c) The hammer strikes the gong producing sound.
(d) Movement of the hammer breaks the circuit, stopping current and demagnetizing the electromagnet.
(e) The spring returns the hammer to original position, closing the circuit again.
This cycle repeats rapidly, causing continuous ringing.
This demonstrates the magnetic effect of electric current and its practical use.

Question 13

Why should electrical appliances not be used with wet hands or near water?

Accepted Answer

Using electrical appliances with wet hands or near water is dangerous because water conducts electricity, increasing the risk of electric shocks and accidents. — Water is a good conductor of electricity. When hands are wet or appliances are near water, electric current can pass through the body causing shocks or injury. Hence, it is a safety measure to avoid such situations.

Question 14

Fill in the blank: When an object gains electrons, it becomes _____ charged.

Accepted Answer

negatively / negative — Electrons carry negative charge. When an object gains electrons, it has excess negative charge and becomes negatively charged.

Question 15

Fill in the blank: The magnetic field lines around a magnet always form _____ loops.

Accepted Answer

closed — Magnetic field lines form continuous closed loops from the north pole to the south pole outside the magnet and through the magnet inside.

SOME NATURAL PHENOMENA

SOME NATURAL PHENOMENA — Study Notes

Introduction

Lightning and Thunder

Electric Charges and Their Effects

Practice Questions — SOME NATURAL PHENOMENA

All 13 Chapters in Science