Physics: Modern Physics: UPSC Previous Year Questions (Science and Technology)
7 previous year UPSC Prelims questions on modern physics are listed here, from 1996 to 2007. UPSC asks how a nuclear chain reaction is sustained, which radiation computed tomography uses, how high a geostationary satellite orbits, how a CD player reads sound and what Dolby noise reduction is. The explanations tie each to the underlying physics.
Explanations state facts as of the year each question was asked; words like “recently” refer to that year.
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UPSC 2007Science and Technology · Physics: Modern Physics
Q1. Which of the following types is used by computed tomography employed for visualisation of the internal structure of the human body?
Explanation
Option (a) is correct: Computed Tomography (CT), also known as a CT scan, uses X-rays to create detailed cross-sectional images of the internal structures of the human body. The X-rays rotate around the body, and a computer processes the data to generate 3D or 2D images. Options (b), (c) and (d) are incorrect:
Sound waves are used in ultrasound imaging not in CT Scans. Magnetic resonance is associated with MRI, which uses magnetic fields and radio waves, not X-rays. Radio isotopes are used in nuclear medicine, such as PET scans.
UPSC 2006Science and Technology · Physics: Modern Physics
Q2. What does the term Dolby B or Dolby C printed on tape- recorders and other sound systems refer to:
Explanation
Option (c) is correct: Dolby B and Dolby C are noise reduction systems developed by Dolby Laboratories to reduce the background hiss (high-frequency noise) in analog audio recordings, such as cassette tapes. These systems work by compressing and expanding certain frequency ranges during recording and playback to enhance audio clarity. Options (a), (c) and (d) are incorrect:
Frequency Modulated System known as FM is a modulation technique used in radio transmissions, not in tape noise reduction. Amplitude Modulated Systems AM is another modulation technique used in radio, unrelated to Dolby noise reduction. Dolby systems are unrelated to power supply types DC and AC.
UPSC 2005Science and Technology · Physics: Modern Physics
Q3. Consider the following statements: 1. A geostationary 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 given above is/are correct?
Explanation
Statement 1 is incorrect: A geostationary satellite orbits the Earth at an altitude of approximately 35,786 km(not 10,000 km) above the equator. This altitude ensures that the satellite’s orbital period matches the Earth’s rotational period, making it appear stationary from the ground.
Statement 2 is correct: FM (Frequency Modulation) is less affected by noise because noise primarily affects amplitude, not frequency. This makes FM transmission superior in quality compared to AM (Amplitude Modulation).
UPSC 2001Science and Technology · Physics: Modern Physics
Q4. Consider the following statements: 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?
Explanation
Nuclear fission is the process in which a heavy atomic nucleus, such as uranium-235 or plutonium-239, splits into two smaller nuclei, releasing a large amount of energy.
Statement 1 is correct: Each fission reaction releases multiple neutrons, which are crucial for sustaining the chain reaction.
Statement 2 is correct: The neutrons produced in fission reactions are used to initiate further fission events.
Statement 3 is correct: Graphite (a moderator) slows down fast neutrons, increasing the likelihood that they will cause further fission reactions, thus making reaction sustainable over longer periods.
Statement 4 is incorrect: Not every neutron released will necessarily cause further fission, as some neutrons may escape the reactor or fail to cause fission if not properly moderated.
UPSC 2000Science and Technology · Physics: Modern Physics
Q5. For reproducing sound, a CD (Compact Disc) audio player uses a:
Explanation
Option (c) is correct: A CD (Compact Disc) audio player uses a laser beam to read the digital information encoded on the surface of the disc. The laser scans the tiny pits and lands that represent the audio data, and the player converts this data into an audio signal. Options (a), (b) and (d) are incorrect:
Quartz crystal: Used in electronic devices like oscillators and watches, but not for sound reproduction in a CD player. Titanium needle: Historically used in turntables or record players (vinyl), not in CD players. Barium titanate ceramic: Used in piezoelectric devices like speakers, but not in reading CDs.
UPSC 2000Science and Technology · Physics: Modern Physics
Q6. Which one of the following does a TV remote control unit use to operate a TV set?
Explanation
A TV remote control typically uses radio waves to communicate with the TV set. Radio waves are a form of electromagnetic radiation that enables the remote to send signals over short distances to control the television. Radio waves are widely used in radio and television broadcasting, enabling the transmission of audio and video signals over long distances. They are also essential in wireless communication systems, including mobile phones, Wi-Fi, and satellite communication. Note: In many sources, infrared waves are identified as the mechanism behind the functioning of TV remote controls, but this option is not provided in the given choices.
Additional insight:
Light waves: Light waves are used in technologies like fiber optics for high-speed internet and communication. Sound waves: Sound waves are used in audio devices, medical imaging (ultrasound), and sonar systems. Microwaves: Microwaves are used in radar, satellite communications, and cooking (microwave ovens).
UPSC 1996Science and Technology · Physics: Modern Physics
Q7. Consider the following statements: 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. Of these statements
Explanation
The industrial ages gave us the understanding of sunlight as an energy source. India is endowed with vast solar energy potential. About 5,000 trillion kWh per year energy is incident over India’s land area with most parts receiving 4-7 kWh per sqm per day. Solar photovoltaic power can effectively be harnessed providing huge scalability in India.
Statement 1 is correct: Solar water heaters are widely used for residential purposes.
Statement 2 is correct: Solar-powered pumps are increasingly utilized for small-scale irrigation. Governments under PM KUSUM are advocating for proliferation of such pumps.
Statement 3 is correct: Solar street lights are common in both rural and urban areas.
Statement 4 is correct: Solar microgrids and standalone systems can provide electricity to remote villages and small towns.
Answer key for these questions
Q
UPSC year
Correct answer
1
2007
(a) X-ray
2
2006
(c) noise Reduction Circuit
3
2005
(b) 2 only
4
2001
(a) 1, 2 and 3
5
2000
(c) laser beam
6
2000
(d) Radio waves
7
1996
(a) 1, 2, 3 and 4 are correct
What UPSC has tested in Physics: Modern Physics
Computed tomography uses X-rays to visualise internal organs.
A CD audio player uses a laser beam to reproduce sound.
Dolby B and Dolby C on tape recorders denote noise reduction circuits.
In a nuclear reactor, a self-sustained chain reaction is possible because more neutrons are released in each fission, and they take part in further fission.
Frequently asked questions
How many previous year UPSC questions are there on Physics: Modern Physics?
This page covers 7 previous year UPSC Prelims GS Paper-I questions on Physics: Modern Physics (Science and Technology), asked from 1996 to 2007. Each has the correct answer and an explanation.
Which radiation does computed tomography use?
X-rays. A CT scanner takes many X-ray images from different angles and combines them by computer into cross-sectional pictures of the body, which gives a far clearer view than an ordinary X-ray.
How does a CD player reproduce sound?
A laser beam scans the track of tiny pits on the disc. The reflected light changes with the pits, and the player converts those changes into an electrical signal that becomes sound.
