How does the atmosphere act as a blanket?
The atmosphere acts as a blanket by performing the following functions:
(a) Ozone absorbs harmful UV radiations coming from the Sun.
(b) Carbon-dioxide and water vapours trap the heat and regulate the temperature of the Earth by keeping it ambient by absorbing heat rays during the day and by reflecting the heat trapped during the daytime at night.
(c) It slows down the escape of heat from the surface of the Earth into outer space during night time.
Therefore, the atmosphere covers and protects the Earth like a blanket.
List any three human activities that you think would lead to air pollution.
What causes winds?
Why is the atmosphere essential for life?
Why do organisms need water?
Why is water essential for life?
We know that many human activities lead to increasing levels of pollution of the air, water-bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollution?
List any three human activities which would lead to an increase in the carbon dioxide content of air.
How is our atmosphere different from the atmospheres on Venus and Mars?
You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?
What is the greenhouse effect?
Which of the following has more inertia: (a) a rubber ball and a stone of the same size? (b) a bicycle and a train? (c) a five-rupees coin and a one-rupee coin?
State the universal law of gravitation.
Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.
A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force (Fig. 11.3). Let us take it that the force acts on the object through the displacement. What is the work done in this case?
What is meant by a pure substance?
How does the sound produced by a vibrating object in a medium reach your ear?
In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
What are canal rays?
State any two conditions essential for good health.
Who discovered cells, and how?
What precautions can you take in your school to reduce the incidence of infectious diseases?
Which organelle is known as the powerhouse of the cell? Why?
A sound wave travels at a speed of 339 m s-1. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?
A trolley, while going down an inclined plane, has an acceleration of 2 cm s-2. What will be its velocity 3 s after the start?
What are the differences between amphibians and reptiles?
What is the role of epidermis in plants?
Describe Bohr’s model of the atom.
The volume of a 500 g sealed packet is 350 cm3. Will the packet float or sink in water if the density of water is 1 g cm-3? What will be the mass of the water displaced by this packet?
The volume of 50 g of a substance is 20 cm3. If the density of water is 1 g cm-3, will the substance float or sink?
Gravitational force on the surface of the moon is only 1/6 as strong as gravitational force on the earth. What is the weight in newtons of a 10 kg object on the moon and on the earth?