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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7- Environment std-4 science

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Time to answer

1. The waste material which can be decomposed by microbes in the soil are called biodegradable waste

2.Non- biodegradable wastes pollute the soil

3.plastics and glass should be thrown in blue bins for recycling. 
1. Multiple choice questions (MCQs) 
Tick(√) the correct option. 

Ans. 1.Air pollution

Ans. 3.water pollution

Ans. Plastic cup

Ans. 3.brain

Q2. Fill in the blanks. 
a. Soil pollution badly affects the growth of crops/ plant. 

b. Smoke causes Air pollution. 

c. We should not use plastic bags as they are nob-biodegradable. 


a. Two living components of your environment
1.plants      2.animals

b. Two natural phenomena that cause air pollution
1.wild fires         2.volcanic eruption

c. Two biodegradable wastes. 
1.paper     2.carbon

d. Two sources of noise pollution
1.vehicles  2.land speaker

4.Read the following two statements and choose the correct option.
Statement1 - organic manure is less harmful than chemical fertilisers. 
Statement2. Overgrazing is one of the causes of soil erosion. 
Ans. a. Both statements 1&2 are correct.
 

a. Why should we use traditional natural fertilisers? 
Ans. We should use traditional natural fertilisers becausethey improve long term soil health which are environmently friendly and cost effective. 

b. What are no horn zone? 
Ans. No hirn zone means the areas where blowing of horns is strictly prohibited. 

c. Why should we not cut down trees? 
Ans. We should not cut trees because they help in a. Purifying air b. Providing shelter to animals and birds c. Preventing soil pollution. 

Q6. Long answer type questions
Ans. 1.Tree help in purifying the air 2. More trees should be planted to reduce soil pollution because trees help prevent soil erosion and maintain the groundwater stable. 
3. Planting trees along roads, hospitals etc reduces noise to a considerable extent. 

Ans. People living in noisy areas are found to have poor hearing abilities. Sound louder than 80 decibels are considered potentially dangerous for human ear. They can also cause nervous disorders. We control noise pollution by planting trees along road, hospital etc it reduce nise to a considerable extent. Blowing of horn should be strictly prohibited near hospital and school. Machinery should be designed in such a way that it makes less noise. Loudspeaker blaring out loud  music and powerful stereo system in cars are already prohibited by low. This law should be enforced mare strictly. 

Ans. Air is naturally by volcanic eruptions and forest fires. Air pollution is mainly cosed by chemical pollutants released from factories power plants, vehicles like car, buses and trucks, domestic cooking, burning of fuels etc. 

Ans. Air pollution can cause cancer, trouble in breathing ( asthma), problema in the lungs and the brain, nerve damage, burning sensation in eyes, etc some of the pollutants are so harmful that they can cause death. 

Ans. Way to control air pollution 
1.we should plant more trees. 
2.factories and industries should be shiftee to remote areas. 
3. Vehicles should be regularly chacked for harmful emissions. 
Way to control water pollution
1. We should not throw garbage and poisonous chemicals into water bodies
2. Industrial waste or domestic sewage should be treated before it is discharged into rivers. 
3. Natural insecticides such as bioneem should be used since it does not harm the environment
4. We should reduce the use of plastics. 


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