12. Light and sound

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12. Light and sound Fill in the blanks.  1. Objects which cannot give out their own light are called Non - luminous.  2. Trandparent   object allow light to pass through them completely.  3. Reflection   is bouncing back of light from a smooth shiny surface.  Write true or false.  1. Sound does not require any medium to travel. (F)   2.The sound of loudspeaker is an unpleasant sound. (T)  3.sound travels through air in the form of particles. (F)  Let us practise 1. Fill in the blanks.  a. Noise is produced by irregular    sound waves.  b. Sun is the main source of heat and light on earth.  c. When light hits a surface and cannot pass through it, the surface is called opaque.  d. Sound is produced due to vibration of objects.  2 . Write 'T' for true and 'F' for false.  a. Honking car is an example of a pleasant sound. (F)  b. Light cannot bend around the cornera. (T)   c. Wat...
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10.Solids, liquids and gases

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10. Solid liquid and gases
Q. 5.Read the following two statements and choose the correct option. 
Statement1- liquid have definite volume and shape. 
Statement 2- The molecules of solid are not very closely packed. 
Ans. Both statements 1 and 2 are incorrect. 

Q6. Short answer type questions
Ans. Melting of butter is a physical change as no new substance is fromed and there is only change in the state of matter on cooling the melted butter gets solidified. 

Ans. We can change a matter from its one state to another by heating and cooling. 

Ans. When solutes ( suger or salt) dissolve in solvent like water, the mixture then formed is known as solution for example ,sugar inbwater salt in water etc. 

Ans. The liquid in which other substancea can dissolve are called solvents. The substance which dissolve in solvents are called solutes. 

Ans. The physical change is a change in the state of matter, but nothing it's identify. A physical change does not produce a new substances. Changes in the state for example melting, freezing, vaporisation condensation, etc are physical change. 

Q7. Long answer type questions
Ans. Matter exists in three stated depending on the arrangement of particles inna substance. Solid, liquid, gas. 
Solid- it has a definite shape and volume ex- steel bar, plastics and ice. 
Liquid- it has a definite volume. They take the shape of the container in which they are keep ex - water, milk and oil
Gas- it has neither a definite volume nor a definite shape. Ex- gases air, oxygen, hydrogen etc. There are two features of state of matter are shape and volume. 

Ans. Physical change:- 
1.it is reversible
2.it is temporary change. 
3. It does not produce a new substance
4. Ex- crushing a can, melting of ice, melting of candle wax. 

Chemical changes
1. It is irreversible 
2. It is permanent change. 
3. It produce a new substance. 
4. Ex- burning of wood, bouled eggs, Rusting of iron nails. 

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