Discover a curated collection of UPSC Prelims topic-wise questions on Physics, focusing specifically on Modern Physics. This resource provides a comprehensive set of questions covering key concepts such as quantum mechanics, relativity, atomic and nuclear physics, and particle physics. Each question is meticulously designed to help aspirants deepen their understanding and proficiency in Modern Physics topics relevant to the UPSC Preliminary Examination. By engaging with these questions, candidates can enhance their problem-solving skills, critical thinking abilities, and overall exam preparedness. Whether you’re a novice or a seasoned aspirant, this resource offers a structured approach to mastering Modern Physics concepts and maximizing your chances of success in the UPSC Prelims. Dive into this invaluable resource to refine your knowledge and excel in the Physics segment of the UPSC examination.
Q1. Which one of the following can be used to confirm whether drinking water contains a gamma emitting isotope or not? (1995)
(a) Microscope
(b) Lead plate
(c) Scintillation counter
(d) Spectrophotometer
Ans. (c)
Option (c), the scintillation counter, is the appropriate tool to confirm the presence of a gamma-emitting isotope in drinking water. This device detects and measures ionizing radiation, particularly gamma rays, by registering the light pulses generated upon interaction with the detector material. It’s commonly used in radiation detection and environmental monitoring.
Q2. The difference between a nuclear reactor and an atomic bomb is that (1995)
(a) no chain reaction takes place in nuclear reactor while in the atomic bomb there is a chain reaction
(b) the chain reaction in nuclear reactor is controlled
(c) the chain reaction in nuclear reactor is not controlled
(d) no chain reaction takes place in atomic bomb while it takes place in nuclear reactor
Ans. (b)
The difference between a nuclear reactor and an atomic bomb lies in the control of the chain reaction. In a nuclear reactor, the chain reaction is managed and controlled, allowing for sustained and controlled energy production. On the other hand, in an atomic bomb, the chain reaction is uncontrolled, leading to a rapid and explosive release of energy. Option (b) correctly highlights this distinction, emphasizing the controlled nature of the nuclear reactor’s chain reaction.
Q3. The technique used to transmit audio signals in television broadcasts is (1995)
(a) Amplitude Modulation
(b) Frequency Modulation
(c) Pulse Code Modulation
(d) Time Division Multiplexing
Ans. (b)
The transmission of audio signals in television broadcasts primarily utilizes Frequency Modulation (FM). Unlike Amplitude Modulation (AM), FM keeps the carrier wave’s amplitude constant while varying its frequency to encode the audio signal. This makes FM less susceptible to amplitude-based noise interference, resulting in clearer audio transmission. Therefore, option (b) is the correct choice.
Q4. Which one of the following elements is essential for the construction of nuclear reactors? (1998)
(a) Cobalt
(b) Nickel
(c) Zirconium
(d) Tungsten
Ans. (c)
Zirconium is indispensable for the construction of nuclear reactors, particularly in the form of nuclear fuel assemblies. It possesses unique properties such as transparency to neutrons, high-temperature stability, and corrosion resistance, making it an ideal material for containing and moderating nuclear reactions. Thus, option (c) accurately identifies zirconium as an essential element in nuclear reactor construction.
Q5. Which one of the following does a TV remote control unit use to operate a TV set? (2000)
(a) Light waves
(b) Sound waves
(c) Micro waves
(d) Radio waves
Ans. (d)
TV remote control units operate using radio waves to communicate with television sets. Radio waves, characterized by their longer wavelengths and ability to penetrate obstacles, provide an effective means of transmitting control signals between the remote and the TV set. Therefore, option (d) correctly identifies radio waves as the medium used by TV remote control units.
Q6. 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?
(a) 1, 2 and 3
(b) 1 and 3
(c) 2 and 4
(d) 2, 3 and 4
Ans. (a)
The self-sustained chain reaction in a nuclear reactor relies on several factors, including the production and utilization of neutrons. Options (1), (2), and (3) highlight key aspects of this process, such as the release of more neutrons in each fission reaction, the prompt involvement of these neutrons in subsequent fissions, and the role of moderators like graphite in slowing down fast neutrons to sustain the chain reaction. Therefore, option (a) accurately represents the conditions necessary for a self-sustained chain reaction in a nuclear reactor.
Q7. Consider the following statements. (2002)
1. Light of longer wavelength is scattered much than the light of shorter wavelength.
2. The speed of visible light in water is 0.95 times the speed in vacuum.
3. Radio waves are produced by rapidly oscillating electrical current.
4. To detect the over speeding vehicles, police use the Doppler effect of reflected short radio waves.
Which of these statements are correct?
(a) 1 and 2
(b) 1 and 3
(c) 2 and 4
(d) 3 and 4
Ans. (d)
Statements (3) and (4) provide accurate insights into the behavior of light and radio waves. Radio waves are indeed generated by rapidly oscillating electrical currents, and the Doppler effect of reflected short radio waves is utilized by police radar to detect over-speeding vehicles. Therefore, option (d) correctly identifies these statements as accurate descriptions of light and radio wave phenomena.
Q8. Consider the following statements (2005)
1. A geo-stationary satellite is at an approximate height of 1000 km.
2. FM transmission of music is a 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?
(a) Only 1
(b) Only 2
(c) Both 1 and 2
(d) Neither 1 nor 2
Ans.(b)
Statement (2) is accurate. FM transmission of music delivers high-quality sound due to its immunity to atmospheric or man-made noise, which often manifests as frequency variations. Unlike AM transmission, FM transmission is resilient against such noise, as noise typically involves amplitude variations caused by factors like atmospheric conditions or industrial interference. Statement (1), however, is erroneous. A geostationary satellite orbits Earth at an approximate altitude of 3600 km, revolving from West to East in a plane aligned with the equator. These satellites play a crucial role in reflecting TV signals and facilitating the transmission of TV programs across different parts of the globe.
Q9. In which one of the following areas did the Indira Gandhi Centre for Atomic Research make significant progress in the year 2005? (2006)
(a) Reprocessing the uranium-plutonium mixed carbide fuel of the Fast Breeder Test Reactor
(b) New applications of radioisotopes in metallurgy
(c) A new technology for production of heavy water
(d) A new technology for high level nuclear waste management
Ans (a)
In 2005, significant strides were made by the Indira Gandhi Centre for Atomic Research in reprocessing the uranium-plutonium mixed carbide fuel of the Fast Breeder Test Reactor. Despite fast neutrons’ limited efficacy in causing fission, they readily interact with a uranium isotope (U238), converting it into Pu239. This plutonium isotope can be reprocessed for use as additional reactor fuel or in the production of nuclear weaponry. The reactor, known as a Fast Breeder Nuclear Reactor, represents a key advancement in nuclear technology.
Q10. What does the term Dolby B or Dolby C printed on tape-recorders and other sound systems refer to? (2006)
(a) Frequency modulated system
(b) Amplitude modulated system
(c) Noise reduction circuit
(d) Both DC and AC power can be used
Ans. (c)
The term “Dolby B” or “Dolby C” found on tape recorders and similar sound systems denotes a noise reduction circuit developed by Dolby Laboratories for analog magnetic tape recording systems. Dolby A and Dolby SR were tailored for professional applications, while Dolby B, C, and S were designed for consumer use.
Q11. Assertion (A) Radiowaves bend in a magnetic field. Reason (R) Radiowaves are electromagnetic in nature. (2008)
Codes
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Ans. (d)
Assertion (A) is false, but the reason (R) is accurate. Radio waves are indeed electromagnetic in nature. They lack an inherent charge and therefore do not interact with charged particles like electrons. Instead, radio waves consist of oscillating electric and magnetic fields perpendicular to their direction of propagation. Consequently, radio waves do not bend in a magnetic field.
Q12. Which one of the following laser types is used in a  laser printer? (2008)
(a) Dye laser
(b) Gas laser
(c) Semiconductor laser
(d) Excimer laser
Ans . (c)
Semiconductor lasers, also known as diode lasers, are employed in laser printers due to their ability to be incorporated into larger arrays functioning as writing sources. Unlike solid-state lasers, semiconductor lasers are electronic devices characterized by their compact size and low power consumption. Today, semiconductor lasers, leveraging materials akin to those in transistors, integrated circuits, and light-emitting diodes, dominate the laser market.
Q13. Which one among the following has the highest energy? (2009)
(a) Blue light
(b) Green light
(c) Red light
(d) Yellow light
Ans. (a)
Blue light boasts the highest energy among the options provided. According to the equation E = hv = hc/λ, where E represents energy, h is Planck’s constant, v denotes frequency, c stands for the speed of light, and λ signifies wavelength, lower wavelengths correspond to higher energy levels. Therefore, blue light, with its shorter wavelength, exhibits the highest energy.
Q14. Which one of the following types of waves are used in a night vision apparatus? (2009)
(a) Radiowaves
(b) Microwaves
(c) Infrared waves
(d) None of these
Ans. (c)
Infrared waves are utilized in night vision apparatuses owing to their capacity to emit heat. Night vision technology enables vision in low-light conditions through a combination of sufficient spectral and intensity ranges. Night Vision Devices (NVDs), containing infrared image intensifier tubes within robust casings, are commonly employed by military personnel. Increasingly, civilian applications of night vision technology, including filming, photography, nocturnal observation, marine navigation, and security, are becoming more prevalent. Some vehicle manufacturers integrate portable night vision cameras into their automobiles for added safety and visibility.
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