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NCERT Exemplar · Class 10 Science Sources of Energy

29 questions · 29 still being checked

Short Answer Questions 16–22 (part 3 of 4)

  1. Exercise 16

    Why is there a need to harness non-conventional sources of energy? Give two main reasons.

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    NCERT’s answer
    Hint—
    (i)
    Our demand for energy is increasing to improve quality of life and growth of population.
    (ii)
    Fossil fuels are limited.
    Energy demand keeps rising with population growth and a better standard of living.
    Fossil fuels (coal, petroleum, natural gas) are non-renewable; reserves are limited and depleting.
    Burning them releases \(\displaystyle \mathrm{CO_2}\), \(\displaystyle \mathrm{SO_2}\), \(\displaystyle \mathrm{NO_x}\): global warming, acid rain.
    Answer: Rising energy demand, and limited, fast-depleting fossil-fuel reserves.

  2. Exercise 17

    Write two different ways of harnessing energy from ocean.

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    NCERT’s answer
    Hint— Tidal, Wave, OTEC etc.
    Tidal energy: a barrage across a narrow estuary traps sea water at high tide; released through turbines at low tide, the flow drives generators.
    Wave energy: the up-and-down motion of waves near the shore drives oscillating/floating devices coupled to turbines.
    Answer: Ocean energy is harnessed as tidal energy (barrage turbines run by the rising/falling tide) and as wave energy (turbines driven by wave motion).

  3. Exercise 18

    What steps would you suggest to minimise environmental pollution caused by burning of fossil fuels?

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    (i)
    Use of smokeless appliances.
    (ii)
    Afforestation
    Use smokeless appliances and well-tuned engines for complete combustion: less \(\displaystyle \mathrm{CO}\) and soot.
    Fit catalytic converters: \(\displaystyle \mathrm{CO}\), \(\displaystyle \mathrm{NO_x}\), hydrocarbons \(\displaystyle \to\) safer gases.
    Switch to cleaner fuels (CNG, unleaded petrol) and scrub flue gases.
    Plant trees: they absorb \(\displaystyle \mathrm{CO_2}\).
    Replace fossil fuels with renewables where possible.
    Answer: Complete combustion, catalytic converters, cleaner fuels, afforestation, renewables.

  4. Exercise 19

    What is the role of a plane mirror and a glass sheet in a solar cooker?

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    NCERT’s answer
    Hint— Plane mirror acts as a reflector, Glass sheet results in green house effect.
    Plane mirror: the tilted lid-mirror reflects extra sunlight into the box, concentrating more radiation on the black tray than direct sun alone. Glass sheet: passes incoming short-wave sunlight but blocks the longer infrared re-radiated by the tray, trapping heat inside (greenhouse effect) and cutting convective loss.Answer: The mirror reflects extra sunlight in; the glass sheet traps re-radiated heat by the greenhouse effect, raising the cooker's temperature.

  5. Exercise 20

    Mention three advantages of a solar cell?

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    NCERT’s answer
    Hint—
    (i)
    Solar cells have no moving parts
    (ii)
    Requires little maintenance
    (iii)
    They can be set up in remote areas
    No moving parts: little maintenance, long working life.
    Converts sunlight directly to electricity, no fuel needed, no pollution or noise.
    Works reliably at remote/inaccessible sites (satellites, calculators, off-grid villages) with no supply line.
    Answer: Solar cells need little maintenance, run pollution- and noise-free without fuel, and work wherever conventional power lines cannot reach.

  6. Exercise 21

    What is biomass? What can be done to obtain bio-energy using biomass?

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    NCERT’s answer
    Hint— Biomass: Plant and animal wastes. Explain the working of a biogas plant with a labelled diagram.
    Biomass is organic matter -- wood, crop residue, animal dung, other biodegradable refuse -- usable as fuel. Bio-energy: dung slurry fed into a biogas-plant digester is anaerobically decomposed by bacteria, releasing biogas (mainly \(\displaystyle \mathrm{CH_4}\)) under a floating dome, while spent slurry drained out serves as manure.Answer: Biomass yields bio-energy through anaerobic digestion in a biogas plant, giving \(\displaystyle \mathrm{CH_4}\)-rich biogas as fuel and spent slurry as manure.

  7. Exercise 22

    What are the limitations in obtaining energy from wind?

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    NCERT’s answer
    Because of it being erratic, energy cannot be harnessed continuously. Large areas are required for wind farms.
    Needs steady wind above about \(\displaystyle 15\ \mathrm{km\,h^{-1}}\) year-round; few sites qualify.
    A windmill farm needs a large area of open land.
    Installation cost is high relative to power obtained.
    No wind, no output -- back-up storage is still needed.
    Blades and towers can harm birds and add noise.
    Answer: Wind needs a steady high-speed site, large land, high cost, back-up for calm spells, and can harm birds.