Physics (Part-II) (UPSC)

Total Questions: 60

41. The technique used to transmit audio signals in television broadcasts is: [1995]

Correct Answer: (b) Frequency Modulation
Solution:Frequency modulation It is a process in which the frequency of the carrier is varied in accordance with the instantaneous value of modulating voltage. In telecommunications and signal processing, frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency. FM is most commonly used for radio and television broadcasting.

42. Consider the following statements: [1996]

At the present level of technology available in India, solar energy can be conveniently used to:

1. Supply hot water to residential buildings.

2. Supply water for minor irrigation projects.

3. Provide street lighting.

4. Electrify a cluster of villages and small towns.

Correct Answer: (c) 1 and 3 are correct
Solution:Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. At present solar energy in our country is used for solar water heater. Solar lights that charge during the day and light up at night are a common sight along walkways.

Solar energy holds significant importance due to its numerous benefits and contributions to a sustainable future. Its significance can be summarized as follows:

  • Renewable and Sustainable: Solar energy is inexhaustible and available worldwide, making it a reliable long-term energy solution.
  • Environmentally Friendly: Reduces greenhouse gas emissions and air pollution, combating climate change and preserving ecological balance.
  • Energy Independence: Reduces reliance on finite fossil fuels and foreign energy sources, promoting energy security.
  • Cost-Effective: Decreases electricity bills and operational costs, especially with advancements in technology and decreasing installation costs.
  • Versatile Applications: Powers diverse systems, from residential and commercial electricity needs to rural electrification and industrial operations.
  • Job Creation and Economic Growth: Drives employment opportunities in manufacturing, installation, and maintenance of solar systems.
  • Improved Quality of Life: Provides access to electricity in remote areas, supporting development and enhancing living standards. By harnessing the sun's abundant energy, solar power contributes to a cleaner, greener, and more resilient future.

43. One astronomical unit is the average distance between : [1998]

Correct Answer: (a) Earth and the Sun
Solution:An astronomical unit (AU) is defined specifically as the average distance between the Earth and the Sun, approximately 93 million miles or 150 million kilometres. The other options are incorrect because the AU does not pertain to the distances between the Earth and the Moon, Jupiter and the Sun, or Pluto and the Sun.
About International Astronomical Union (IAU)
  • It was founded in 1919 as a senior body governing international professional astronomical activities worldwide.
  • Its mission is to promote and safeguard the science of astronomy in all its aspects, including research, communication, education, and development, through international cooperation.

Activities:

  • Definition of fundamental astronomical and dynamical constants and unambiguous astronomical nomenclature
  • Rapid dissemination of new discoveries
  • Organization of international observing campaigns
  • Promotion of educational activities in astronomy to early informal discussions of possible future international large-scale facilities.
  • It is the only organization recognized professionally for the naming of astronomical bodies, which it does solely on the basis of merit, history, or discoverer’s privilege.
  • The IAU holds a general assembly every three years in varying parts of the world. The long-term policy of the IAU is defined by the General Assembly.
  • Headquarters: Paris, France.

44. For reproducing sound, a CD (Compact Disc) audio player uses a: [2000]

Correct Answer: (c) laser beam
Solution:The laser beam reads the digital data encoded on the CD's surface by reflecting off pits and lands on the disc. This data is then converted into an audio signal. The other options are incorrect: a quartz crystal is used in timekeeping, a titanium needle is used in record players, and barium titanium ceramic is not used in CD players.

45. Which one of the following to operate a TV set? [2001]

Correct Answer: (d) Radio waves
Solution:Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Like all other electromagnetic waves, they travel at the speed of light.

Artificially-generated radio waves are used for fixed and mobile radio communication, broadcasting, radar and other navigation systems, satellite communication, computer networks and innumerable other applications.

46. Consider the following statements: [2001]

In a nuclear reactor, self-sustained chain reaction is possible, because:

1. more neutrons are released in each of the fission reactions.

2. the neutrons immediately take part in the fission process.

3. the fast neutrons are slowed down by graphite.

4. every neutron released in the fission reaction initiates further fission.

Which of these statements are correct?

Correct Answer: (b) 1 and 3
Solution:In a nuclear reactor, more neutrons are indeed released in each fission reaction, and these fast neutrons are slowed down by a moderator like Graphite to sustain the chain reaction. Statement 2 is incorrect because neutrons do not immediately take part in the fission process; they need to be slowed down first. Statement 4 is also incorrect because not every neutron initiates further fission; some escape or are absorbed without causing fission.

47. Consider the following statements: [2005]

1. A geo-stationary satellite is at an approximate height of 10,000 km.

2. FM transmission of music is of very good quality because the atmospheric or man made noises which are generally frequency variations can do little harm.

Which of the statements give above is/are correct?

Correct Answer: (b) 2 only
Solution:The geostationary satellite is a satellite having a time-period of 24 hours. Using this time-period, the height of the satellite comes out to be approximately 35,800 km. FM broadcasting is a broadcast technology pioneered by Edwin Howard Armstrong that uses frequency modulation (FM) to provide high-fidelity sound over broadcast radio. FM transmission is quite immune to noise as compared to AM transmission. Noise is a form of amplitude variations in the transmitted signal due to atmosphere, industries, etc.

48. What does the term Dolby B or Dolby C printed on tape-recorders and other sound systems refer to: [2006]

Correct Answer: (c) noise Reduction Circuit
Solution:Dolby B and C are the noise reduction circuits developed by Dolby laboratories. Dolby noise reduction has made it possible to protect the music from tape noise, and helped make cassette the most popular audio product ever devised.

In 1965 electrical engineer Dr. Ray Dolby (b. 1933) proposed the first magnetic tape noise reduction system The task was to improve the signal-to-noise ratio of the recording, reducing the level of hiss without affecting the quality of the sound. His approach was to "compand" (compress, then expand) the sound. During recording, an encoding circuit was inserted between the recording source and the tape recorder; this compressed the dynamic range of the recording. During playback, a decoding circuit was inserted between the tape recorder and the playback amplifier, expanding the dynamic range once again. The quieter sounds in the spectrum received a greater proportional boost; the signal level dropped and was filtered in the higher frequencies (where the tape hiss existed). On playback the white noise was less audible. Dolby's first system, Dolby A, was widely adopted within the professional recording market. When the lower- fidelity Philips cassette replaced the reel-to-reel machine, Dolby produced a simpler version and licensed it to cassette recorder manufacturers

49. Which of the following types is used by computed tomography employed for visualisation of the internal structure of human body? [2007]

Correct Answer: (a) X-ray
Solution:X-ray computed tomography (CT) is a medical imaging method employing tomography created by computer processing. This technique is used to generate a three-dimensional image of the inside of an object.
X-rays are a type of electromagnetic radiation, falling between ultraviolet (UV) light and gamma rays on the electromagnetic spectrum. They have shorter wavelengths and higher frequencies than visible light, which gives them high energy. This high energy allows X-rays to penetrate many materials, which is why they are widely used in medical imaging and material inspection.
Properties of X-Rays
Wavelength: Approximately 0.0101 to 1010 nanometers.
Frequency: Between 3x1016x1016 Hz and 3x1019x1019 Hz.
Energy: Typically between 100100 eV and 100100 keV, which is strong enough to ionize atoms in the matter they penetrate.

50. With reference to solar power production in India, consider the following statements: [2018-1]

1. India is the third largest in the world in the manufacture of silicon wafers used in photovoltaic units.

2. The solar power tariffs are determined by the Solar Energy Corporation of India.

Which of the statements given above is/are correct?

Correct Answer: (d) Neither 1 nor 2
Solution:There is no significant production of silicon wafers in India (as of 2011). So unlikely that it became 3rd largest by 2017-18. So, #1 is wrong.

Tariff's are determined under the Electricity Act. Any entity with "Corporation" word is irrelevant. so, #2 is wrong.