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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11.soil erosion

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11.Soil Erosion
Time to Answer

Full in the blanks. 
1.Removal of fertile topsoil is soil erosion. 
2.The two natural agents of soil erosion are wind   and water. 
3. Large - scale cutting down of forests is known as deforation . 
4.plants take nutrients from soil. 

Write true or false. 
1. Soil conservation is the protection of soil from erosion. 
Ans. True
2.Afforestation is large scale cutting down of trees. 
Ans. False
3. Power plants are built on rivers to control force of flood water. 
Ans. False
4. Overgrazing should be prevented to avoid soil erosion. 
Ans. True
5. The practice of terrace farming helps to reduce soil erosion. 
Ans. True. 
 

Match the following. 
a. Organisms living in soil =soil life
b. Earthworm= Farmers friend
c. Crop rotation= Improves fertility of soil
d. Crop= plants grown by farmers
Q4. Short answer type questions
Ans. Terrace farming is the method of growing crops on the sides of hills or mountains by planting on graduated terraces built into the slope. 

Ans. Overgrazing is the exposure of a piece of land to excessive grazing by herbivores without allowing the vegetation to recover. 

Ans. Soil is important as it contains the nutrients required for the growth of plants. It is also a shelter for a wide range animals. 

Ans. Soil life is a collective term for all the organisms living in the soil. Plants and animals are dependent on another and on the soil in which they live. 
Q5. Long answer type questions
Ans. There are two main causes of soil erosion water and wind. 
*soil erosion by water- soil in hilly areas is washed away by rainwater and rivers and is carried down to the plants. This soil deposits on organic matter and is very fertile. 
*Soil erosion by wind- The fertile to soil is blown away by strong winds and gets deposited other places. 
It's effect are:
1.It washes away the fertile top soil making land barren and unproductive. 
2.It also deposits unwant sand and other types of soil over the productive soil. 

Ans. To increase crop yields, the farmer adds some substances to the soil. These substance make the soil fertile by increasing the minerals and humus content crops use these nutrients to grow faster, bigger and better. 

Ans. Growing different crops on the same field in rotation is called crop rotation, crop rotation gives the soil time to replenish the minerals and nutrient that have been used up by the previous crop. 
Crop rotation has a great important in crop fields. It helps in increasing the fertility pf the soil. It does not lead to depletion of nutrients from the soil. 

Ans-It is a dam. 

Ans. The main purpose of dam construction is to control the force of excess water and prevent soil erosion caused by flooding. 

Ans. Floods cause a great damage to soil through soil erosion so, dam are built across rivers to control the force of flood water which helps in soil erosion. 

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