12. Light and sound

Image
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...

8.our solar system

science std 4
Stateboard question with ans. 
Time to Answer
Fill in  the blanks. 
1. Mercury is the smallest planet. 
2.Venus is also known as the morning star. 
3.Moon is a heavenly body that moves around planets. 
4.Mars is also called the red planet. 
5.Jupiter is the largest planet. 


Fill in the blanks. 
1.The Rotation of the earth causes day and night. 
2.The revolution of the earth causes seasons
3. The sunbrises from east and sets in the West
4.The outermost hard layer of the earth is called crust

5. Short answer type questions
Ans. Orbit is a curved path followed by a planet or an object as it moves around another planet, star, moon etc
Ans. 
.         Star                                  planet                  .
1.They are big               1.They are slow moving
   heavenly bodies          heavenly bodies that                                                move in an orbit                                                      around the sun.         . 
2. Sun is the only star   2.They are only 8 planet
Present in the solar         in the solar system
System .                                                                 . 
3.They have their own  3. They do not have 
heat and light.                  light of their own.       . 

Ans. Saturn and Jupiter have more than 60 moons. 

Ans. Our earth complete one revolution in 365 1/14 days, which is called asolar year. 

6.Long answer types questions
Ans. Scientists believe that the earth was a huge ball of dust and burning gasses in the beginning. It kept on spinning,. As it spun around for millions of years, it's outer surface became cold and hard some of the hot gasses escaped, while some were trapped inside. So the outer surface of the earth is hard but the inside has hot molten material this is how the earth come into existence. 

Ans. The earth crust is made up of rocks and mineral. It is also coverd with oceans and seasy and farms and living beings. 

Ans. The revolution of the earth causes seasons. The earth revolves around the sun how ever during it's revolution, it's axis always remains tilted at an angel. As a result, at certain times of the year, the North Hemisphere is tilted towards the sun, while the southern Hemisphere is tilted away from it. At other times, the southern Hemisphere is tilted towards the sun, while the Northern Hemisphere is tilted away from it. The hemisphere which is tilted towards the sun gets the sun's rays directly & so it is warmer than the other hemisphere which is tilted away from the sun gets slanting rays from the sun & has winter. 

d. Why is the season in the Northern Hemisphere always different from that in the southern Hemisphere? 
Ans. The season in the northern hemisphere is always different from that in the southern hemisphere because of the following resons. 
1. When the North hemisphere is tilted to wards the sun it has summer. At there time the southern hemisphere tilted away from the sun has winter. 
2. When the northern hemisphere is tilted away from the sun it has winter & the southern hemisphere has summer. 

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