Chapter 1 – Earth As a Planet | Class 9 School Geography Solution

Book Name	: School Geography
Subject	: Geography
Class	: 9 (Madhyamik)
Publisher	: Bengal Book Syndicate (P) Ltd.
Chapter Name	: Earth As a Planet

Identify the correct answers

Question 1 (a)

The round shape of the earth was first proved by Aristotle / Galileo / Ferdinand Magellan / Kepler.

Answer

The round shape of the earth was first proved by Aristotle.

Question 1 (b)

The shadow of the earth cast on the moon during eclipses is square /  rectangular / conical / round in shape.

Answer

The shadow of the earth cast on the moon during eclipses is round in shape.

Question 1 (c)

The difference between the equatorial diameter and the polar diameter is 62 Km /42km / 56 Km / 90 Km.

Answer

The difference between the equatorial diameter and the polar diameter of the Earth is approximately 42 kilometers or 26 miles.

Question 1 (d)

The horizon of the earth seems to widen with decreasing altitude / decreasing length / increasing altitude / increasing length.

Answer

The horizon of the Earth seems to widen with increasing altitude.

Question 1 (e)

When we watch a ship approaching the harbour we first see the whole ship / the bottom of the ship / the top of the mast / the hull.

Answer

When we watch a ship approaching the harbour, the first part of the ship we see is the top of the mast or the highest point of the ship.

Question 1 (f)

At the equator, the length of 1° of latitude is 110.58 km / 117.4 km. / 150.18 Km / 111.32 Km.

Answer

At the equator, the length of 1° of latitude is approximately 111.32 kilometres or 69.17 miles.

Question 1 (g)

The shape of the earth looks like that of an apple / a pear / a guava / a pineapple.

Answer

The shape of the earth looks like that of a pear

Question 1 (h)

Jupiter is about 9.444 / 11.209 / 3.883 / 2.032 times bigger than the earth.

Answer

Jupiter is about 11.209 times bigger than the Earth.

Question 1 (i)

The English word ‘Eartha’ means table / ground / book / ball.

Answer

The English word ‘Eartha’ means ground.

Question 1 (j)

The circumference of the earth was first measured by Hadley / Holmes / Eratosthenes / Ferrel.

Answer

The circumference of the Earth was first measured by Eratosthenes.

If the sentence is true write T and if false write F against the following

1. Earth has a layer of air surrounding it composed of 21% Nitrogen and 50% Oxygen and the rest of carbon dioxide.
2. Jupiter keeps the large rocks away from the earth by its strong gravity.
3. The core of the Earth has silica and iron.
4. The circumference of the Earth is about 40,000 Km.
5. The Bedford Level experiment was performed by Bedford.
6. The term Geoid means ‘earth shaped’.

Answer

1. False; The statement is incorrect. The Earth’s atmosphere is actually composed of approximately 78% nitrogen, 21% oxygen, and 1% other gases, including carbon dioxide.
2. True
3. True
4. True
5. False; The Bedford Level experiment was conducted by Samuel Birley Rowbotham, who used the pseudonym “Parallax.”
6. True

Fill in the blanks with appropriate words

1. Around 350 B.C. the great ____ first declared that the earth was round.
2. At 45° latitude, an observer finds the North Star ____ between the zenith and the horizon.
3. Aeroplanes can fly around the Earth following ____ ____.
4. The shape of the Earth with two flattened ends and a bulge at the equator is called an ____ ____.

Answer

1. Aristotle
2. Midway
3. Mercator, Chart
4. oblate spheroid.

Answer in words or words

Question 4

1. Who first observed the Earth’s shape as an oblate spheroid?
2. Where on Earth is the weight of an object measured by a spring balance, the greatest?
3. What is the length of Earth’s Polar diameter?
4. What determines the size of a planet?
5. What are the large holes on the surface of the moon called?
6. What is the full form of GPS?

Answer

1. Jean Richer
2. Earth’s pole
3. 12,713 km
4. Diameter
5. craters
6. Global Positioning System

Match the column

Question 5

Answer

Short answer type questions

Question 6

1. Write in short about the Earth as an oblate spheroid. 
2. Give two proofs of Earth’s sphericity
3. What is GPS? 
4. Discuss briefly Earth’s unique position in the Solar System.
5. Why is Earth considered the home of humankind?
6. Why there is a bulge in the equatorial region?

Answer

1. The Earth is not a perfect sphere, but it is flattened at the poles and bulges at the equator, making it an oblate spheroid. This shape is caused by the Earth’s rotation, which causes the equator to bulge outwards due to centrifugal force.
2. Two proofs of Earth’s sphericity are the observation of the curved shadow of the Earth during lunar eclipses and the fact that ships disappear over the horizon due to the curvature of the Earth.
3. GPS stands for Global Positioning System. It is a satellite-based navigation system that uses a network of satellites orbiting the Earth to determine the precise location and time information of a GPS receiver. The GPS system is maintained by the United States government and can be used for a wide range of applications, including navigation, mapping, surveying, and tracking.
4. Earth’s unique position in the Solar System is due to its location in the habitable zone, where temperatures are suitable for the existence of liquid water, and the presence of a protective magnetic field and atmosphere that shields the planet from harmful solar radiation.
5. Earth is considered the home of humankind because it is the only planet known to support life. Its environment provides the necessary conditions for the existence and evolution of a wide range of organisms, including humans.
6. The bulge at the equatorial region is due to the Earth’s rotation, which causes the equator to bulge outwards due to centrifugal force. This results in the equatorial diameter of the Earth being larger than the polar diameter.

Answer the following questions

Question 7 (a)

Write three proofs to show that the Earth is round.

Answer

1. Ship’s hull disappearing: As a ship sails away from an observer on a flat surface, it eventually disappears from the bottom up. This happens because the Earth’s surface curves away from the observer, making the ship appear to sink lower into the water until it disappears.
2. Lunar eclipses: During a lunar eclipse, the Earth’s shadow can be seen on the surface of the moon. The shape of the shadow is curved, indicating that the Earth is round.
3. Travelling in different directions: If someone travels in different directions, they will eventually end up back where they started. This is only possible on a curved surface, like a sphere.

Question 7 (b)

How did Eratosthenes calculate the circumference of the Earth?

Answer

Eratosthenes was a smart person who lived a long time ago. He figured out how big the Earth was by using the sun and a stick. He saw that in one place, the sun was straight above a deep hole, but in another place, the sun was at an angle and made a shadow. He measured the angle of the shadow and used math to find out how big the Earth was. He found that it was around 39,375 kilometres, which is close to what we know today.

Question 7 (c)

Why is Earth’s shape considered as a Geoid? 

Answer

The shape of the Earth is considered as a geoid because it is not a perfect sphere, but rather an irregular shape where the gravitational pull is different in different regions. The geoid is a three-dimensional representation of the Earth’s gravitational field and takes into account the bulges and depressions in the planet’s shape. This shape is caused by a combination of the Earth’s rotation, the distribution of mass, and the gravitational pull of the Sun and Moon. As a result, the Earth’s shape is best described as a geoid, a term that comes from the Greek word “geo” meaning Earth, and “eidos” meaning form or shape.

Question 7 (d)

Discuss the size of the Earth in proportion to the other planets.

Answer

The size of Earth is relatively small compared to some of the other planets in our solar system, such as Jupiter and Saturn. Earth has a diameter of about 12,742 kilometres, which makes it the fifth-largest planet in the solar system. Jupiter, on the other hand, has a diameter of about 142,984 kilometres, which is more than 11 times the size of Earth.

Cross-Word

Question 8

Across-

(1) He proved Earth’s curvature on Bedford canal, England.

(4) Short form of Global Positioning System.

(5) One of the two cities of Egypt, where Eratosthenes conducted an experiment.

Down-

(2) The shape of the Earth with polar flattening and equatorial bulge.

(3) The Greek mathematician who first measured the Earth’s circumference.

Answer

Across: (1) Bedford (4) GPS (5) Alexandria

Down: (2) Oblate spheroid (3) Eratosthenes

Long answer or essay-type questions

Question 9 (a)

Discuss the proofs of Earth’s round shape.

Answer

There are several proofs that demonstrate that the Earth is round:

1. Observing a ship’s hull: As a ship approaches the horizon, its hull disappears before the top of its mast. This happens because the Earth curves away from us, and the bottom of the ship disappears first. If the Earth were flat, the entire ship would be visible until it became too small to see.
2. Lunar eclipses: During a lunar eclipse, the Earth casts a curved shadow on the moon. The shape of the shadow is always circular, regardless of where the observer is on Earth. This is possible only if the Earth is round.
3. Travelling in a straight line: If someone travels in a straight line on the surface of the Earth, eventually they will end up back where they started. This is only possible if the Earth is a closed, spherical shape.

These proofs have been recognized for thousands of years and were first studied and explained by ancient Greek scholars, such as Aristotle and Eratosthenes. Today, we have advanced technology like satellites and GPS that further confirm the roundness of our planet.

Question 9 (b)

With the help of a diagram explain why the Earth is called a geoid.

Answer

The Earth is called a geoid because its shape approximates a mathematical model of the Earth’s surface known as a geoid. A geoid is a three-dimensional representation of the Earth’s shape, which takes into account variations in the planet’s gravity field and the distribution of mass throughout its interior.

The Earth’s shape is not a perfect sphere due to the gravitational forces exerted by its rotation, which cause it to bulge at the equator and flatten at the poles. These irregularities in the Earth’s shape cause variations in the planet’s gravitational field, which in turn affect the Earth’s surface features like mountains, oceans, and continents. The geoid provides a more accurate representation of the Earth’s shape, which is important for surveying, navigation, and other scientific purposes.

Question 3

Describe how Eratosthenes calculated Earth’s circumference.

Answer

Eratosthenes, an ancient Greek mathematician and astronomer, calculated the circumference of the Earth in 240 BC. He noticed that at noon on the summer solstice, the sun shone directly down a deep well in the city of Syene (modern-day Aswan in Egypt), causing no shadow. At the same time, in Alexandria, Egypt, which was due north of Syene, the sun was at an angle, creating a shadow.

Eratosthenes measured the angle of the shadow using a gnomon (a vertical rod), and used his knowledge of geometry to calculate the angle of the sun’s rays. By using the distance between Alexandria and Syene, which he obtained from camel caravans, he was able to calculate the circumference of the Earth to be approximately 39,375 kilometres, which is very close to the modern measurement of 40,075 kilometres.

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