Question

Geo-stationary satellite is one which
A. Remains stationary at a fixed height from the earth's surface.
B. Revolves like other satellites but in the opposite direction of earth's rotation.
C. Revolves around the earth at a suitable height with same angular velocity and in the same direction as earth does about its own axis.
D. None of these

Answer 1

- Hint-In order to solve this question, we must know what is a geo-stationary satellite and what are its properties. Then we will compare each option with the properties of a geo-stationary satellite to get the appropriate answer.

Complete step-by-step solution -

Firstly, we must know the concept of a geo-stationary satellite so that we can get the right answer.
Geo- stationary is a satellite in geosynchronous orbit with an orbital period the same as the earth’s rotation period. Geo- stationary satellites are also known as synchronous satellites.
Geo-stationary satellites have the unique property of remaining permanently fixed in exactly the same position in the sky as viewed from any fixed location on earth. This means that it remains stationary at a fixed height from the earth’s surface. This property also implies that ground-based antennas do not need to track them but can remain fixed in one direction. These satellites are used for communication purposes that form a geosynchronous network.
Geo-stationary satellites always remain about the same path on the equator i.e. it has a period of exactly one day (86400).
The orbit radius $\left[ {T = 2\pi \sqrt {\dfrac{{{r^3}}}{{GM}}} } \right]$ comes out to be 42400 km, which is nearly equal to the circumference of earth.
Height of the geostationary satellite from the earth surface is 42,400 – 6400 = 36,000km.
After knowing the concept, we came to an end that-
Option 2 i.e. it revolves like other satellites but in the opposite direction of earth’s rotation.
Option 3 i.e. it revolves around the earth at a suitable height with same angular velocity and in the same direction as earth does about its own axis.
These options are not involved in the concept of geo-stationary satellites.
Therefore, option A i.e. it remains stationary at a fixed height from the earth’s surface is right as we already know this unique property- Geo-stationary satellites have the unique property of remaining permanently fixed in exactly the same position in the sky as viewed from any fixed location on earth.

Note- While solving this question, we must know the concept of binding energy and satellites. Binding energy of satellites is the minimum amount of energy required to be supplied to free the satellite from the gravitational influence of the earth. Along with that, we must try to know unique properties of satellites to solve this problem and similar problems.