General Science PYQ – Heat, Light and Sound
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There is no Doppler effect when the source-listener distance does not change; a source moving towards a listener at rest does produce it, so statement 1 is false.
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General Science PYQ – Heat, Light and Sound – 33 questions, subject: Science. Every question has the correct answer with a one-line explanation; tap "Show Answer". Free practice for TNPSC, UPSC, SSC, Bank and RRB exams – Shanmugam IAS Academy, Coimbatore.
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1.
Executive Officer Gr. III (HR&CE) 2022
The minimum possible temperature beyond which matter cannot be cooled isCorrect Answer: C [–273°C]
Explanation:
Absolute zero, 0 K or -273.15 degrees C, is the lowest possible temperature, below which matter cannot be cooled.
2.
PTGS 2021
The snow on the mountains does not melt all at once when it is heated by the sun becauseCorrect Answer: B [it has high latent heat of fusion]
Explanation:
Ice has a high latent heat of fusion, so a large amount of heat is needed to melt it without a temperature rise, and snow melts slowly.
3.
Reporter 2022
Let the boiling temperature of water in a pressure cooker be T. ThenCorrect Answer: D [T > 100°C]
Explanation:
Pressure in a pressure cooker exceeds atmospheric pressure, which raises the boiling point of water above 100 degrees C.
4.
Reporter 2022
Food cooks faster in a pressure cooker than in an ordinary pot with a loose lid because the higher pressureCorrect Answer: C [raises the boiling point of water]
Explanation:
The higher pressure in a pressure cooker raises the boiling point of water, so food cooks at a higher temperature and faster.
5.
Fisheries Inspector / SI 2023
At higher altitude, the boiling point of a substance willCorrect Answer: A [decrease]
Explanation:
At higher altitudes atmospheric pressure is lower, so the boiling point decreases.
6.
Group 1B/1C 2024
On a cold morning, a metal surface will feel colder to touch than a wooden surface because the metal hasCorrect Answer: C [High thermal conductivity]
Explanation:
Metal is a good conductor of heat, so it draws heat from the hand quickly and feels colder than wood at the same temperature.
7.
(i) Conduction
(ii) Convection
(iii) Radiation
District Educational Officer 2023
Heat transfer in a transparent solid is by(i) Conduction
(ii) Convection
(iii) Radiation
Correct Answer: D [(i) and (iii) only]
Explanation:
In a transparent solid there is no convection, and heat moves by conduction and by radiation passing through, so (i) and (iii) are correct.
8.
District Educational Officer 2023
The contraction of volume when ice melts can be attributed toCorrect Answer: A [Partial collapse of tetrahedral structure]
Explanation:
In ice, water molecules are held in an open tetrahedral hydrogen-bonded structure, and when it partly collapses on melting, the volume contracts.
9.
Reporter 2022
A perfectly black body is that whichCorrect Answer: D [absorbs all the radiations incident on it]
Explanation:
A perfect black body absorbs all radiation falling on it and reflects none.
10.
Fisheries Inspector / SI 2023
Pyrometer works on ______ law.Correct Answer: A [Stefan's law]
Explanation:
A pyrometer measures temperature from the radiation emitted by a hot body, based on Stefan's law (energy radiated proportional to T^4).
11.
EO Group VII (HR&CE) 2022
The refrigerator and ice plant work under the principle ofCorrect Answer: B [Second law of thermodynamics]
Explanation:
A refrigerator works on the second law of thermodynamics: heat cannot flow from cold to hot unless external work is done.
12.
GSASO 2020
Blue colour of sky is due toCorrect Answer: D [scattering of light]
Explanation:
The sky looks blue because atmospheric molecules scatter short-wavelength blue light more strongly (Rayleigh scattering, proportional to 1/wavelength^4).
13.
1. Rayleigh scattering: Scattering of sunlight by atoms or molecules of gases in the atmosphere
2. Mie scattering: Inelastic scattering caused by pollen, dust, smoke and other particles in the lower atmosphere
3. Tyndall scattering: Scattering of light rays by colloidal particles in the colloidal solution
4. Raman scattering: When sunlight passes through a gas or liquid the entire light is scattered by the atmosphere
Special Competitive Exam 2025
Which of the following statements are incorrect?1. Rayleigh scattering: Scattering of sunlight by atoms or molecules of gases in the atmosphere
2. Mie scattering: Inelastic scattering caused by pollen, dust, smoke and other particles in the lower atmosphere
3. Tyndall scattering: Scattering of light rays by colloidal particles in the colloidal solution
4. Raman scattering: When sunlight passes through a gas or liquid the entire light is scattered by the atmosphere
Correct Answer: B [2 and 4]
Explanation:
Mie scattering by larger particles is elastic, so calling it inelastic is wrong, and the keyed fourth statement is also wrong, so statements 2 and 4 are incorrect.
14.
AHGS 2021
The colour of light that travels through glass with minimum speed isCorrect Answer: A [Violet]
Explanation:
Violet light has the highest refractive index in glass, so by v = c/n it travels with the lowest speed.
15.
Group 2/2A 2024
Green light shines on a (red) rose flower. Then, the colour of its petals seems to beCorrect Answer: C [Black]
Explanation:
A red rose reflects only red light and absorbs green, so under green light it reflects almost nothing and looks black.
16.
Asst. Conservator of Forests 2023
The colours exhibited in soap bubbles are due to the ______ of light.Correct Answer: C [Interference]
Explanation:
The colours in soap bubbles arise from interference between light reflected from the upper and lower surfaces of the thin film.
17.
GSASO 2020
If light waves emitted by two coherent sources have wavelengths λ1 and λ2 thenCorrect Answer: A [λ1 = λ2]
Explanation:
Coherent sources emit light of the same wavelength and constant phase difference, so lambda1 equals lambda2.
18.
Reason (R): Polarising angle is the angle of incidence for which the reflected light is completely plane polarised.
Asst. Conservator of Forests 2023
Assertion (A): Light incident on a surface at a polarising angle of 40° will have the same angle of incidence 40°.Reason (R): Polarising angle is the angle of incidence for which the reflected light is completely plane polarised.
Correct Answer: C [Both (A) and (R) are true; and (R) is the correct explanation of (A)]
Explanation:
At the polarising (Brewster) angle the reflected light is completely plane polarised, and it is the angle of incidence, so an angle of 40 degrees means incidence of 40 degrees and R explains A.
19.
Group 1 2022
Quantum nature of light is not supported by the phenomenon ofCorrect Answer: D [Interference of light waves]
Explanation:
Photoelectric effect, Compton effect and atomic spectra support the quantum nature of light, whereas interference shows only its wave nature.
20.
Health Officer 2023
The power of lens is measured inCorrect Answer: A [Diopter]
Explanation:
The power of a lens, P = 1/f with f in metres, is measured in dioptres.
21.
VCGS 2022
A convex lens of power 3 dioptre and a concave lens of power 2 dioptre are combined together. Then the equivalent power isCorrect Answer: B [Convex lens of 1 dioptre]
Explanation:
Powers of lenses in contact add, so +3 D plus -2 D equals +1 D, a convex lens of 1 dioptre.
22.
Asst. Director (Fisheries) 2022
The radiation with highest energy isCorrect Answer: A [X-ray]
Explanation:
Photon energy E = h x frequency, and X-rays have the highest frequency among the options, so they have the highest energy.
23.
Combined Accounts Service 2024
Who discovered X-rays?Correct Answer: D [Roentgen]
Explanation:
Wilhelm Conrad Roentgen discovered X-rays in 1895 and won the first Nobel Prize in Physics in 1901.
24.
Forest Apprentice 2022
Metals with high atomic numbers are used as targets for the production of X-rays. Why?Correct Answer: C [They will give more energetic and intense X-rays]
Explanation:
High atomic number metals like tungsten give more energetic and intense X-rays when struck by fast electrons.
25.
Agricultural Officer 2023
Which of the following molecule(s) causes food to cook in a microwave oven?Correct Answer: C [H₂O]
Explanation:
Water molecules in food absorb microwave radiation and rotate rapidly, and the resulting friction produces the heat that cooks the food.
26.
AD Co-operation 2022
Sound travels at maximum speed inCorrect Answer: A [Steel]
Explanation:
Sound travels fastest in solids, slower in liquids and slowest in gases, and cannot travel in a vacuum, so among the options steel carries it fastest.
27.
GSCE 2021
According to Laplace, sound propagation is an _____ process.Correct Answer: B [Adiabatic]
Explanation:
Laplace showed that compressions and rarefactions in a sound wave occur too quickly for heat exchange, so sound propagation is an adiabatic process, not isothermal as Newton assumed.
28.
ADGS 2021
The velocity of sound in air at 30°C is 350 m/s. Keeping the temperature constant, the pressure of air is doubled. The velocity of sound in air now will beCorrect Answer: C [350 m/s]
Explanation:
The speed of sound in a gas depends on temperature, not pressure, since the P/rho ratio stays constant, so it remains 350 m/s.
29.
PSY 2022
When mechanical waves have a frequency below the audible range, these are calledCorrect Answer: B [Infrasonics]
Explanation:
Mechanical waves below 20 Hz, the lower limit of human hearing, are called infrasonics, while those above 20 kHz are ultrasonics.
30.
Asst. Director (Fisheries) 2022
Decibel is a unit to measure theCorrect Answer: B [Intensity of sound]
Explanation:
The decibel (dB) is the unit of sound intensity level, with 0 dB marking the threshold of hearing.
31.
CTS (Interview Posts) 2024
The frequency of a siren increases as it comes near you and then diminishes as it passes away, but it remains the same inside the ambulance. What is the reason?Correct Answer: A [Doppler effect]
Explanation:
The change in frequency heard due to relative motion between source and listener is the Doppler effect, higher on approach and lower on receding.
32.
(1) Doppler effect in light is symmetric
(2) Doppler effect in sound is symmetric
(3) Doppler effect in light is asymmetric
(4) Doppler effect in sound is asymmetric
Group 1 2022
Which of the following is/are true about Doppler effect?(1) Doppler effect in light is symmetric
(2) Doppler effect in sound is symmetric
(3) Doppler effect in light is asymmetric
(4) Doppler effect in sound is asymmetric
Correct Answer: B [(1) and (4) are correct]
Explanation:
Doppler effect in light is symmetric as it depends only on relative velocity, while in sound it is asymmetric because it depends on whether source or observer moves; so (1) and (4) are correct.
33.
1. Listener at rest and source moves towards the listener
2. S and L move in such a way that distance between them remains constant
3. S and L are moving in mutually perpendicular directions
4. The source is situated at the centre of the circle along which the listener is moving
Group 4 2024
Which of the following statements is false about "conditions for no Doppler effect"?1. Listener at rest and source moves towards the listener
2. S and L move in such a way that distance between them remains constant
3. S and L are moving in mutually perpendicular directions
4. The source is situated at the centre of the circle along which the listener is moving
Correct Answer: A [1 only]
Explanation:
There is no Doppler effect when the source-listener distance does not change; a source moving towards a listener at rest does produce it, so statement 1 is false.
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