Physics (Part-II) (UPSC)

Total Questions: 60

51. Consider the following phenomena : [1995]

1. Light is affected by gravity.

2. The Universe is constantly expanding.

3. Matter warps its surrounding space-time.

Which of the above is/are the prediction/predictions of Albert Einstein's General Theory of Relativity, often discussed in media?

Correct Answer: (d) 1, 2 and 3
Solution:2010: International Team of Astronomers confirmed Albert Einstein's theory of general relativity and that the expansion of the universe is accelerating after looking at data from the Hubble Space Telescope. There is an unknown source of energy in the universe which is causing the cosmic expansion to speed up. 2016: Japanese researchers' study finds that the expansion of the universe could be explained by a cosmological constant, as proposed by Einstein in his theory of general relativity. So second statement is right. This eliminates B and (C).

2018: Hubble Space Telescope captured image of a phenomenon called Einstein Ring. Einstein in his theory of general relativity, had suggested that a massive object would warp space and time. So, statement3 is right. Hence we are left with correct answer "ID": 1, 2 and 3 all correct.

52. Cryogenic engines find applications in: [1995]

Correct Answer: (c) rocket technology
Solution:A cryogenic rocket engine is a rocket engine that uses a cryogenic fuel or oxidiser, that is, its fuel or oxidizer (or both) are gases liquefied and stored at very low temperatures. Notably, these engines were one of the main factors of the ultimate success in reaching the Moon by the Saturn V rocket. Various cryogenic fuel-oxidizer combinations have been tried, but the combination of liquid hydrogen fuel and the liquid oxygen oxidizer is one of the most widely used.

53. Consider the following statements: [1996]

A person in a spaceship located half way between the earth and the sun will notice that the:

1. sky is jet black.

2. stars do not twinkle.

3. temperature outside the spaceship is much higher than that on the surface of the earth.

Correct Answer: (d) 1, 2 and 3 are correct
Solution:There is a presence of atmosphere at earth's surface which consists of thick and moving layers of air. The dust particles, particulates, smog, water vapour and smoke are also present in air. Stars twinkle when we see them from the Earth's surface because we are viewing them through thick layers of turbulent (moving) air in the Earth's atmosphere. As their light travels through the many layers of the Earth's atmosphere, the light of the star is bent (refracted) many times in random directions (light is bent when it hits a change in density-like a pocket of cold air or hot air). This random refraction results in the star as its twinkling but for a person in spaceship no such refractions are possible as there is vaccum in space. Thus, star will not twinkle.

Similarly, sky will appear blue to us due to Rayleigh scattering which is again due to presence of atmosphere on earth's surface. The shorter wavelength light is absorbed by the gas molecules of atmosphere. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Some of this scattered blue light reaches you. Since, you see, the sky looks blue. Whereas no atmosphere is there in space thus, no absorbing and scattering is possible that's why for a person in spaceship sky appears black.

Temperature outside the spaceship is higher in comparison to earth's surface because of being nearer to sun.

54. The tail of a comet is directed away from the sun because: [1997]

Correct Answer: (c) the radiation emitted by the sun exerts a radial pressure on the comet throwing its tail away from the sun
Solution:

The radiation emitted by sun exerts a radial presssure on the comet. So the tail of comet is always directed away from the sun.
• Comets are frozen leftovers from the formation of the solar system composed of dust, rock and ices.
• These icy objects, occasionally pushed by gravity into orbits bringing them closer to the Sun, become the so-called short-period comets.
• The astronomer Gerard Kuiper gave a theory in 1951, a disc-like belt of icy bodies exists beyond Neptune, where a population of dark comets orbits the Sun in the realm of Pluto.
• They range from a few miles to tens of miles wide, but as they orbit closer to the sun, they heat up and spew gases and dust

55. A 'black hole' is a body in space which does not allow any radiation to come out. This property is due to its: [2000]

Correct Answer: (c) very high density
Solution:A black hole is a region of space from which nothing, not even light, can escape. It is the result of the deformation of spacetime caused by a very compact mass. The simplest black hole has mass but neither electric charge nor angular momentum.

The mass of a black hole is finite, the reason why a black hole has infinite density is that it's mass is concentrated into a space of zero-volume. Thus, it has a very high density.

In 2019, the Event Horizon Telescope (EHT) collaboration released the first image of a black hole. The image shows the sudden loss of photons (particles of light).

56. Consider the following statements in respect of India advanced satellite INSAT-4A: [2006]

1. INSAT-4A was launched in December, 2005 from New Mexico.

2. The European Commercial Launch Service Provider Arianespace was associated with the launch of INSA T-4A.

3. Tata-Sky; a digital cable service provider, is associated with DTH television broadcasting service from INSA T 4A.

Which of the statements given above are correct?

Correct Answer: (c) 2 and 3 only
Solution:Statement '2' and '3' is correct, but 'l' is incorrect. Because INSAT-4A was launched on 22 December 2005 from French Guiana.
INSAT Satellite
• With nine operational communication satellites in Geo-stationary orbit, the Indian National Satellite (INSAT) system is one of the largest domestic communication satellite systems in the Asia-Pacific region.
• With the launch of INSAT-1B in 1983, it launched a major revolution in India’s communications sector that has since been sustained.
• With over 200 transponders in the C, Extended C, and Ku bands, the INSAT system supports telecommunications, television broadcasting, satellite newsgathering, societal applications, weather forecasting, disaster warning, and Search and Rescue operations.
• The INSAT system revolutionised television and radio broadcasting, telecommunications, and meteorology in India.
• It facilitated the rapid expansion of television and modern telecommunications facilities to remote areas and offshore islands.
• Master Control Facilities located in Hassan and Bhopal monitor and control the satellites.

57. Consider the following statements in respect of a jet engine and a rocket: [2008]

1. A jet engine uses the surrounding air for its oxygen supply and so is unsuitable for motion in space.

2. A rocket carries its own supply of oxygen in the gas form, and fuel.

Which of the statements given above is/are correct?

Correct Answer: (c) Both 1 and 2
Solution:

Ajet engine combines oxygen from the air with fuel at high temperature. There is usually a spark to ignite the fuel vapor, but once the engine begins turning, it will continue running until it runs out of fuel or air. A rocket, carries its own supply of liquid oxygen for combustion.
• Jet engines and rockets work on the same principle they produce thrust through an internal pressure difference and as explained by Newton’s 3rd law of motion eject exhaust gases in an equal and opposite direction.
• The main differences are while jets get the oxygen to burn fuel from the air and rockets carry their own oxygen which allows them to operate in space. Jet engines have 2 openings, an intake and exhaust nozzle whereas rocket engines only have one opening, an exhaust nozzle.

58. Satellites used for telecommunication relay are kept in a geostationary orbit. A satellite is said to be in such as orbit when: [2011-1]

1. The orbit is geosynchronous.

2. The orbit is circular.

3. The orbit lies in the plane of the earth's equator.

4. The orbit is at an altitude of 22,

Select the correct answer using the codes given below:

Correct Answer: (a) 1, 2 and 3 only
Solution:A geostationary orbit (or Geostationary Earth Orbit - GEO) is a geosynchronous orbit directly above the Earth's equator (0° latitude), with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. It is the part of space about 35,786 km (22,236 miles) above sea level, in the plane of the equator, where near-geostationary orbits may be implemented.

59. An artificial satellite orbiting around the Earth does not fall down. This is so because the attraction of Earth : [2011-1]

Correct Answer: (d) provides the necessary acceleration for its motion
Solution:An artificial satellite moving round the Earth in a circular orbit possesses an acceleration which is "constant" in magnitude but "changing in direction". An artificial satellite revolves round the earth under centripetal acceleration. By the launch rocket, immediately before the satellite is established in the predetermined orbit, the speed given to it is 30, 000 km/hr. The speed must be great enough so gravity doesn't bring the satellite back to Earth, but not so great that the satellite escapes gravity out into space. This means that the speed, which is provided by the rocket is the source of the centrifugal force, and the attraction of the earth holds it from moving away from this centrifugal force.

60. In which of the following activities are Indian Remote Sensing (IRS) satellites used? [2015-1]

1. Assessment of crop productivity

2. Locating groundwater resources

3. Mineral exploration

4. Telecommunications

5. Traffic studies

Select the correct answer using the code given below.

Correct Answer: (a) 1, 2 and 3 only
Solution:Indian Remote Sensing (IRS) satellites are used in Assessment of crop productivity, Locating ground-water resources and Mineral exploration. This system was launched in 1979 and 1981.

This system is used in agriculture, water resources, forestry and ecology, geology, marine fisheries and coastal management. It is the largest constellation of the remote sensing satellites.