Q20 of 27 Page 1

(a)What is meant by the term ‘power of accommodation’? Name the component of the eye that is responsible for the power of accommodation.

b. A student sitting at the back bench in a class has difficulty in reading. What could be his defect of vision? Draw ray diagrams to illustrate the image formation of the blackboard when he is seated at the (i) back seat (ii) front seat. State two possible causes of this defect. Explain the method of correcting this defect with the help of a ray diagram.

a. The ability of the eye to focus both near and distant objects, by adjusting its focal length of the eye lens by the action of ciliary

muscles are called as the power of accommodation of the human eye.


The component of the eye which is responsible for the power of accommodation is ciliary muscle.



b.


The student being not able to see the blackboard from the last bench of the rows confirms that the student is suffering from myopia or short-sightedness.


The ray diagram for the image formation of the student when seated at the (i) back seat (ii) front seat are as follow.



The two possible causes of this defect.


1. Either eyeball is longer than normal or.


2. The ciliary muscle which adjusts the focal length of length has become insufficient to adjust the maximum focal length of the eye lens according to the distant object.


This defect can be corrected by using a concave lens of suitable power.


The method of correction is shown in the ray diagram(C).


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18

a) Draw the diagram of the female reproductive system and match and mark the part(s):

i) Where the block is created surgically to prevent fertilization.


ii) Where CuT is inserted?


iii) Inside which condom can be placed.


b. Why do more and more people prefer to use condoms? What is the principle behind the use of condoms?

 19

Name the phenomenon that governs the following: - 5

i) Green beetles living in green bushes are not eaten by the crows.


ii) Number of blue beetles in green bushes increases, only because the red beetles living there were trampled by a herd of elephants.


iii) No ‘medium height plants’ are obtained in F1 generation, upon crossing pure tall and dwarf pea plants.


iv) Tails of mice were surgically removed for several generations; still, mice had tails in the following generations.


v) A migrant beetle reproduces with the local population; as result genes of migrant beetle enter the new population.


OR


a) What are fossils and how is the age of fossils determined?


b). During artificial selection, which features of wild cabbage were selected to give rise to i) Cabbage ii) Cauliflower

 21

(i) With the help of an activity, explain the method of inducing an electric current in a coil with a moving magnet — State the rule used to find the direction of electric current thus generated in the coil.

(ii) Two circular coils-1 and coil-2 are kept close to each other as shown in the diagram.Coil-1 is connected to a battery and key and coil-2with a galvanometer. State your observation in the galvanometer:



a) When key k closed; (b) when key k is opened; Give a reason for your observations.


OR


Name a device which converts mechanical energy into electrical energy. Explain the underlying principle and working of this device with the help of a labelled diagram.

 22

When a few drops of phenolphthalein are added to a dilute solution of sodium hydroxide a pink colour is produced. What will be the colour of the final mixture when an excess of HCl is added to it? (justify your answer)

OR


Arrange the metals iron, magnesium, zinc and copper in the increasing order of their reactivity. What will be the two observations made by the student when iron filings are added to the copper sulphate solution?