This set covers everyday applications of physics and chemistry, from why the sky is blue to how a nuclear reactor works and what common household chemicals are. UPSC often asks about the science behind familiar things, and these questions draw on NCERT-level concepts.
How to practise: read each question and tap the option you think is correct. You will see right away whether you got it, along with a short explanation, and your score is tracked at the bottom of the screen. This set has 15 questions.
Topics covered in this set
- Scattering, refraction and total internal reflection
- Sound, ultrasound and infrasound
- Household electricity and fuses
- Nuclear fission and fusion
- Common chemicals and their formulas
- Hard water, corrosion and ozone
UPSC Science and Technology MCQs with answers and explanations
Q1. The sky appears blue mainly because
a) the ocean reflects blue light into the sky
b) shorter blue wavelengths are scattered much more by air molecules than longer red wavelengths
c) the atmosphere absorbs all other colours
d) sunlight itself contains only blue light
Q2. A rainbow forms because of
a) reflection of sunlight from clouds only
b) diffraction of light by dust particles
c) refraction, dispersion and internal reflection of sunlight in raindrops
d) absorption of sunlight by water vapour
Q3. Optical fibres carry light signals over long distances using the principle of
a) total internal reflection
b) diffraction
c) polarisation
d) photoelectric effect
Q4. Which type of mirror is used as a rear-view mirror in vehicles, and why?
a) Concave mirror, because it gives a magnified image
b) Plane mirror, because it gives an inverted image
c) Concave mirror, because it focuses sunlight
d) Convex mirror, because it gives an upright, smaller image with a wider field of view
Q5. Through which of the following does sound travel fastest?
a) Air
b) Water
c) Steel
d) Vacuum
Q6. Ultrasound is sound with a frequency
a) above about 20,000 Hz, which humans cannot hear
b) below about 20 Hz, which humans cannot hear
c) between 20 Hz and 20,000 Hz
d) equal to the frequency of light
Q7. Which of the following is correct about an electric fuse in a household circuit?
a) It is connected in parallel with the appliance
b) It is made of a wire with a low melting point and melts to break the circuit when current becomes too high
c) It increases the voltage supplied to appliances
d) It is made of a material with a very high melting point
Q8. Household alternating current supply in India is at
a) 110 V and 60 Hz
b) 440 V and 100 Hz
c) 12 V and 50 Hz
d) about 220-230 V and 50 Hz
Q9. In a nuclear reactor, control rods made of boron or cadmium are used to
a) absorb neutrons and regulate the rate of the chain reaction
b) speed up the neutrons
c) cool the reactor core directly
d) produce uranium fuel
Q10. The energy of the Sun is produced mainly by
a) nuclear fission of uranium
b) burning of hydrogen gas with oxygen
c) nuclear fusion of hydrogen nuclei into helium
d) radioactive decay of carbon
Q11. Which of the following chemical name and common name pairs is correctly matched?
a) Sodium hydrogen carbonate - Washing soda
b) Calcium oxychloride - Bleaching powder
c) Calcium sulphate hemihydrate - Baking soda
d) Sodium carbonate decahydrate - Plaster of Paris
Q12. Dry ice, used to keep items very cold, is
a) frozen water mixed with salt
b) liquid nitrogen
c) frozen ammonia
d) solid carbon dioxide
Q13. Temporary hardness of water can be removed by boiling because it is caused by
a) bicarbonates of calcium and magnesium
b) sulphates of calcium and magnesium
c) chlorides of sodium
d) dissolved oxygen
Q14. Galvanisation protects iron from rusting by
a) painting it with oil
b) coating it with a layer of zinc
c) mixing it with carbon
d) heating it to a high temperature
Q15. Why is a strong-smelling compound such as ethyl mercaptan added to LPG?
a) To increase its heating value
b) To make it burn with a blue flame
c) To help detect leaks, since LPG itself is odourless
d) To prevent it from freezing
Quick revision notes
- Rayleigh scattering is strongest for short wavelengths, which makes the sky blue and red light suitable for danger signals.
- Optical fibres and the sparkle of diamonds are both due to total internal reflection.
- Sound travels fastest in solids and cannot travel through a vacuum; ultrasound is above 20,000 Hz.
- India's household supply is about 220-230 V at 50 Hz, and a fuse is connected in series.
- In reactors, moderators slow neutrons and control rods absorb them; the Sun shines by fusion of hydrogen into helium.
- Baking soda is NaHCO3, washing soda is Na2CO3.10H2O, bleaching powder is calcium oxychloride and dry ice is solid CO2.
Frequently asked questions
What is the difference between nuclear fission and fusion?
Fission splits a heavy nucleus such as uranium-235 into lighter nuclei, releasing energy, and is used in current power plants. Fusion joins light nuclei such as hydrogen isotopes into heavier ones, releasing even more energy per unit mass. Fusion produces less long-lived radioactive waste but is very hard to sustain.
Why is heavy water used in Indian nuclear reactors?
India's pressurised heavy water reactors use heavy water as a moderator and coolant. Heavy water absorbs few neutrons, so natural uranium can be used as fuel without enrichment. This suits India's three-stage nuclear programme.
Why do danger signals use red light?
Red light has the longest wavelength in the visible range and is scattered the least. It therefore travels farther through fog, dust and smoke. This makes it visible from a greater distance.
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