Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
(a) Some substances possess the property of sublimation like camphor and naphthalene balls. Such substances directly change from solid to gaseous state without changing in to liquid like:
ice → water → water vapour does.
Therefore, naphthalene balls disappear with time without leaving any solid.
(Sublimation - Solid to gaseous state directly converted).
(b) Being a volatile substance (gets evaporated easily) perfume changes from liquid to gaseous state very fast. Those particles mix up with air particles and diffuse to reach our nostrils such that we get the smell of perfume sitting several metres away.
(volatile substance → liquid to gaseous state changed immediately).
Popular Questions of Class Science
- Q:-
Convert into mole.
(a) 12 g of oxygen gas
(b) 20 g of water
(c) 22 g of carbon dioxide. - Q:-
Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?
- Q:-
Why is the atmosphere essential for life?
- Q:-
Why is the weight of an object on the moon 1/6th its weight on the earth?
- Q:-
What happens to the force between two objects, if
(i) the mass of one object is doubled?
(ii) the distance between the objects is doubled and tripled?
(iii) the masses of both objects are doubled? - Q:-
Why are we normally advised to take bland and nourishing food when we are sick?
- Q:-
You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?
- Q:-
Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?
- Q:-
What are the immunisation programmes available at the nearest health centre in your locality? Which of these diseases are the major health problems in your area?
- Q:-
List any three human activities that you think would lead to air pollution.
Recently Viewed Questions of Class Science
- Q:-
Define the term “tissue”.
- Q:-
Diagrammatically show the difference between the three types of muscle fibres.
- Q:-
What is the utility of tissues in multi-cellular organisms?
- Q:-
If Z = 3, what would be the valency of the element? Also, name the element.
- Q:-
Identify the type of tissue in the following: skin, bark of tree, bone, lining of kidney tubule, vascular bundle.
- Q:-
Differentiate between parenchyma, collenchyma and sclerenchyma on the basis of their cell wall.
- Q:-
You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?
- Q:-
Name A,B,C,D,E and F in the following diagram showing change in its state
- Q:-
Differentiate between striated, unstriated and cardiac muscles on the basis of their structure and site/location in the body.
- Q:-
Where is apical meristem found?
- NCERT Chapter