CBSE Class-10 Exam 2020 : Question Paper (Science)

• Subject : Science
• Time allowed : 3 hours
• Maximum Marks : 80

SECTION A

1. Covalent compounds have low melting and boiling point. Why ? 1
2. How many metals are present in second period of periodic table ? 1 

3. Answer question numbers 3(a) to 3(d) on the basis of your understanding of the following paragraph and the related studied concepts.

Geothermal energy is the energy produced by the heat of molten rocks formed in the deeper hot regions of the earth’s crust. This energy is harnessed to generate electricity. When water is made to flow deep underground in the rocks it returns as steam (or hot water, which is later converted to steam) to drive a turbine on an electric power generator. 

In India, exploration and study of geothermal fields started in 1970. The Geological Survey in India has identified 350 geothermal energy locations in the country. The most promising of these is in Puga valley of Ladakh. The estimated potential for geothermal energy in India is about 10000 MW. There are seven geothermal provinces in India namely the Himalayas, Sohna, West coast, Cambay, Son-Narmada-Tapi; Godavari and Mahanadi. Most power stations in India produce Alternating Current (A.C).
(a) What are geothermal energy hot-spots ? 1
(b) Name two countries, other than India, where power plants based on geothermal energy are operational. 1
(c) Name the phenomenon that explains the working of an electric generator. 1
(d) State an important advantage of using AC over DC. 1

4. Answer question numbers 4(a) to 4(d) on the basis of your understanding of the following information and related studied concepts.

Thyroid gland is a bilobed structure situated in our neck region. It secretes a hormone called thyroxine. Iodine is necessary for the thyroid gland to make thyroxine. Thyroxine regulates carbohydrate, protein and fat metabolism in the body. It promotes growth of body tissues also. When there is an excess of thyroxine in the body, a person suffers from hyperthyroidism and if this gland is underactive it results in hypothyroidism. Hyperthyroidism is diagnosed by blood tests that measure the levels of thyroxine and Thyroid Stimulating Hormone (TSH).  Hypothyroidism is caused due to the deficiency of iodine in our diet resulting in a disease called goitre. Iodised salt can be included in our diet to control it.
(a) Where is thyroid gland situated in our body ? 1
(b) State the function of thyroxine in human body. 1
(c) What is hyperthyroidism ? 1
(d) How can we control hypothyroidism ? 1

5. Consider the following reasons for the reddish appearance of the sun at the sunrise or the sunset :
A. Light from the sun near the horizon passes through thinner layers of air.
B. Light from the sun covers larger distance of the earth’s atmosphere before reaching our eyes.
C. Near the horizon, most of the blue light and shorter wavelengths are scattered away by the particles.
D. Light from the sun near the horizon passes through thicker layers of air.
The correct reasons are
(a) A and C only 
(b) B, C and D
(c) A and B only
(d) C and D only 1

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