CBSE Class 10 Science Advanced Physics Source of Energy Nuclear Fission and Fusion Very Short Answer Questions Set 02

Very Short Answer Type

Question 16. Nuclear fusion is the process of fusion of ____________ nuclei into __________ nuclei.
Answer:
Nuclear fusion is the combining of lighter nuclei into a heavier nucleus.
In simple words: Light nuclei join to make a heavier one.

Teacher's Note:
1. It occurs at very high temperature.
2. Example: d + d gives helium-3.

Question 17. Named the isotopes of uranium present in naturally occurring uranium.
Answer:
Natural uranium contains mainly U-238 (about 99.3%) and a small amount of U-235 (about 0.7%), with a trace of U-234.
In simple words: Mostly U-238 with a little U-235.

Teacher's Note:
1. Only U-235 is easily fissionable by slow neutrons.
2. Isotopes have equal Z but different A.

Question 18. 1 amu = _____________ kg.
Answer:
1 amu = 1.66 × 10^–27 kg.
In simple words: One atomic mass unit is a very small mass.

Teacher's Note:
1. It is equivalent to 931 MeV of energy.
2. Remember the power of ten.

Question 19. Is the energy released per nucleon in fission greater than that released during fusion?
Answer:
No. The energy per nucleon is greater for fusion than for fission.
In simple words: Fusion wins per nucleon.

Teacher's Note:
1. This question was repeated in the exercise.
2. Compare energy per unit mass of fuel.

Question 20. What is a good source of energy?
Answer:
A good source of energy gives a large amount of useful energy, is easy to store and transport, and supplies energy steadily and cheaply with little pollution.
In simple words: A good source gives plenty of useful energy conveniently.

Teacher's Note:
1. List two or three qualities.
2. Cost and pollution matter too.

Question 21. If you could use any source of energy for heating your food, which one would you use and why
Answer:
I would use solar energy (a solar cooker) because it is free, renewable and causes no pollution. (Biogas is another good choice because it burns cleanly.)
In simple words: Choose a clean, renewable source and give a reason.

Teacher's Note:
1. Any sensible answer with a reason is accepted.
2. Mention one limitation if you can.

Question 22. What are the limitations of the energy that can be obtained from the oceans?
Answer:
1. Tidal energy needs special sites for a barrage and the rise and fall of tide is small.
2. Wave energy is available only near coasts and depends on wind.
3. Ocean thermal energy needs a temperature difference of at least 20 °C between the surface and deep water, and the plants are costly.
In simple words: Ocean energy needs special places and costly plants.

Teacher's Note:
1. Give one limitation for each form of ocean energy.
2. Cost and location are the main issues.

Question 23. When we cannot used a solar water heater to get hot water ?
Answer:
A solar water heater cannot be used at night and on cloudy, foggy or rainy days, when little sunlight reaches it.
In simple words: No sunlight means no solar heating.

Teacher's Note:
1. Solar energy is not constant.
2. A backup heater is needed.

Question 24. On what basis would you classify energy sources as (a) renewable and non-renewable? (b) exhaustible and inexhaustible?
Answer:
(a) Renewable sources are replaced by nature continuously and can be used again and again; non-renewable sources cannot be replaced once used.
(b) Inexhaustible sources will never end (Sun, wind); exhaustible sources will be finished one day (coal, petroleum).
In simple words: Whether the source is replaced by nature, and whether it will ever end.

Teacher's Note:
1. The two classifications are very similar.
2. Give an example for each.

Question 25. What is tidal energy ?
Answer:
Tidal energy is the energy of the rising and falling water of the sea caused by the attraction of the moon, and it is used to turn turbines and generate electricity.
In simple words: It is the energy of ocean tides.

Teacher's Note:
1. Same as the earlier tidal energy question.
2. Mention the moon.

Question 26. Write the characteristic features of the micro organisms which help in the production of biogas in a biogas plant.
Answer:
The microorganisms are anaerobic bacteria: they live and work in the absence of oxygen, and they decompose (ferment) cattle dung and other organic wastes in the presence of water to produce methane-rich biogas.
In simple words: Biogas bacteria work without oxygen.

Teacher's Note:
1. Anaerobic means without air.
2. The digester is sealed for this reason.

Question 27. Can you place alcohol under the category of renewable source of energy?
Answer:
Yes. Alcohol (ethanol) is made by fermenting sugar cane and other crops, which can be grown again and again, so it is renewable.
In simple words: Ethanol comes from crops, so it is renewable.

Teacher's Note:
1. Alcohol obtained from petroleum would not be renewable.
2. It has a calorific value of about 30 kJ/g.

Question 28. Name the devices in which solar energy is harnessed directly.
Answer:
Solar cooker, solar water heater, solar cell (panel) and solar furnace.
In simple words: These devices use sunlight without any intermediate form.

Teacher's Note:
1. Include both heating devices and solar cells.
2. Plants and wind use it indirectly.

Question 29. Define nuclear fusion.
Answer:
The process in which two or more light nuclei combine to form a heavier nucleus with the release of a large amount of energy is called nuclear fusion.
In simple words: Light nuclei fuse into a heavier nucleus and give energy.

Teacher's Note:
1. Give an example such as d + d.
2. Mention high temperature.

Question 30. Define nuclear fission.
Answer:
The process in which a heavy nucleus (like uranium-235), when hit by a neutron, splits into two lighter nuclei with the release of neutrons and a large amount of energy is called nuclear fission.
In simple words: A heavy nucleus splits into smaller nuclei and gives energy.

Teacher's Note:
1. Name the Hahn and Strassmann experiment (1939).
2. Three neutrons come out in the Ba–Kr reaction.