Q18 of 40 Page 1

Water is an elixir of life, a very important natural resource. Your Science teacher wants you to prepare a plan for a formative assessment activity, ‘‘How to save water, the vital natural resource’’. Write any two ways that you will suggest to bring awareness in your neighbourhood, on ‘how to save water’.

a. We can save water by

i. By closing the water taps while brushing teeth, shaving, cleaning clothes etc. and repairing leaky pipes and taps to save water.


ii. Harvesting and conserving water.


iii. Stop polluting water and create awareness among people to save water


iv. We can use waste water for gardening, cleaning vehicles etc.


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16

If the image formed by a lens for all positions of an object placed in front of it is always erect and diminished, what is the nature of this lens? Draw a ray diagram to justify your answer. If the numerical value of the power of this lens is 10 D, what is its focal length in the Cartesian system?

 17

State the cause of dispersion of white light by a glass prism. How did Newton, using two identical glass prisms, show that white light is made of seven colours? Draw a ray diagram to show the path of a narrow beam of white light, through a combination of two identical prisms arranged together in an inverted position with respect to each other, when it is allowed to fall obliquely on one of the faces of the first prism of the combination.

 18

Name and explain any one way by which the underground water table does not go down further.

 19

Why are certain compounds called hydrocarbons? Write the general formula for homologous series of alkanes, alkenes, and alkynes and also draw the structure of the first member of each series. Write the name of the reaction that converts alkenes into alkanes and also writes a chemical equation to show the necessary conditions for the reaction to occur.