Lesson: Some Natural Phenomena
Topic 1: Earthquake

# Question: 1

What is an earthquake?

## Solution:

An earthquake is a sudden movement of the earth’s trembling of the earth crust which lasts for a very short time. It is caused by a disturbance deep inside the earth due to a movement of tectonic plates.

# Question: 2

What causes an earthquake?

## Solution:

An earthquake is caused by a sudden disturbance inside the fragmented earth’s crust due to the movement of tectonic plates. It can result in immense loss to life and property.

# Question: 3

What instrument is used to measure the intensity of earthquakes?

## Solution:

The magnitude of the intensity of an earthquake is measured through an instrument called the seismograph.

# Question: 4

Which parts of the earth are more prone to earthquakes?

## Solution:

Earthquakes are caused due to shifting of tectonic plates with respect to one another. The region that lie on the boundaries of these plates, called seismic zones, are more prone to earthquakes than other regions on the earth’s surface.

# Question: 5

List the types of tectonic movement.

## Solution:

There are three types of tectonic movement:

Plates collide with each other

Plates move away from each other

Plates slide along each other

# Question: 6

List the layers of the earth?

## Solution:

The layers of the earth are:

Crust

Mantle

Inner core

Outer core

# Question: 7

What is the uppermost part of the earth? Why is it a bit different?

## Solution:

The uppermost part of the earth is the crust. It is different as it is fragmented and divided into plates which move.

# Question: 8

How much stronger is an earthquake of magnitude 7 compared to an earthquake of magnitude 5 on the Richter scale?

## Solution:

The power of an earthquake is expressed on a scale called Richter scale which is not a linear scale. It is a logarithmic scale which means an increase of 2 in magnitude of an earthquake results in 100 times more destruction. Hence, an earthquake of magnitude 7 is a hundred times stronger than earthquake of magnitude 5.

Topic 2: Lightning

# Question: 1

When we rub a glass rod with a silk cloth what kind of charges do they acquire?

## Solution:

When a glass rod is rubbed with silk, there is a transfer of negative charge from glass to silk and hence the glass rod acquires a positive charge.

# Question: 2

What kind of device can judge whether an object carries charge or not?

## Solution:

Electroscope is a device that helps us to determine whether an object carries charge or not.

# Question: 3

Why does an uncharged object sometimes attract a charged object?

## Solution:

An uncharged object contains an equal number if positive and negative charges. A charged object if brought near an uncharged one repels the like charges in the latter and attracts the unlike ones, thus attracting the uncharged object.

For example, a balloon which has been negatively charged by rubbing it with a piece of cloth sticks to a wall because of an attractive force. This is because the negative in the balloon are attracted to the positive ones while the negative charges in the wall are repelled away.

# Question: 4

What is earthing?

## Solution:

Earthing is the process of neutralising a charged object by transferring its charge to the surface of the earth.

# Question: 5

Explain how lightning occurs.

## Solution:

Lightning takes place when positive and negative charges get built up within a cloud or in different clouds. Due to movement of water droplets and ice particles within the clouds, the clouds get positive charges at the top and negative at the bottom. These charges become very strong and eventually the difference in positive and negative charges overcomes the effect of the insulating atmosphere between them, and the two charges are neutralised with a strong electric current that produces bright light and the sound of thunder. The lightning can occur within a cloud, between different clouds, or between a cloud and the earth.

# Question: 6

How would you protect yourself if you are outside your house and a thunderstorm arrives?

## Solution:

The following precautions should be taken if you are outdoors during a thunderstorm:

Move away from open areas, to somewhere with lots of trees or tall objects

Do not touch these trees or tall objects, as it is possible that the lightning could use them as a way of reaching the earth’s charge

Do not use an umbrella

If in an open field, do not lie on the ground. Instead, sit on your haunches and make yourself as small a target as possible.