Question of Exercise - 1

Light of Class 7

Which mirror used is used in vehicles?


Option 1 Plain mirror

Option 2 Concave mirror

Option 3 Convex mirror

Option 4 None of the above

Frequently Asked Questions

Study the following statements about ozone

(a) It is essential for breathing of living organisms.

(b) It is used to disinfect water.

(c) It absorbs ultraviolet rays.

(d) Its proportion in air is about 3%.

Which of these statements are correct?

(i) (a), (b) and (c)

(ii) (b) and (c)

(iii) (a) and (d)

(iv) All four



Correct Answer : (ii) (b) and (c)

Solution: Ozone is used to disinfect water during wastewater treatment. Ozone is an unstable gas that destroys bacteria and virus.

It also absorbs ultraviolet rays coming from the sun.


Outline your role as an active citizen in relation to sanitation


Ans: Role as an active citizen in relation to sanitation are:

· contribute in maintaining sanitation at public places. We should not scatter litter anywhere.

· Preventing clogging of drains by not releasing oil and fat and solid waste into the drain.

· Ensure that the sewerage system in the house is properly managed.

· Ensure that my surrounding and neighborhood is maintained and help the municipality in maintaining proper sanity

Explain the relationship between sanitation and disease


Ans: Sanitation and disease are related to each other because poor sanitation is the cause of large number of diseases. The Untreated human excreta are a health hazard. It pollutes soil and water sources including groundwater. Groundwater is a source of water for wells, tube wells, springs and many rivers. When this polluted water is used for drinking, it can cause water-borne diseases including cholera, typhoid, polio, meningitis, hepatitis and dysentery.

Therefore, lack of sanitation resulting in drinking of polluted water can cause health problems.

Explain the function of bar screens in a wastewater treatment plant


Ans: Bar screens are large filters which are placed in the form of vertical screens. This is used in wastewater treatment to remove large objects like rags, sticks, cans, plastic packets, napkins

Name two chemicals used to disinfect water


Ans: Two chemicals used to disinfect water are Ozone and chlorine.

Ozone: Ozone has great actions against bacteria and virus.

Chlorine: It is highly effective disinfectant.

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