7. Lenses | Science I | Class 10

The blog presents the important question and answers from chapter 07, Lenses from Class 10, Maharashtra State Board. The students can study from these notes to understand and score good marks in Board exams.

Q4. Give scientific reasons:

(a) Simple microscope is used for watch repairs.

Ans. A simple microscope is used for watch repairs because :
(i) A microscope has a convex lens and when an object is placed within the focal length a larger and erect is obtained on the same
side of the lens.
(ii) When the watch repairer uses the microscope by adjusting the distance between the object and the lens he gets the image at the minimum disance of distinct vision.
(iii) As a result the watch repairer can see the minute parts of the watch more clearly than with naked eye without any stress on the
eyes.

(b) One can sense colours only in bright light.

Ans. (i) In the eyes the retina is made of many light sensitive cells.
(ii) In the retina has two types of cells i.e. the rod-shaped and the cone-shaped cells. The rod-shaped cells repond to the intensity of
light while the cone-shaped cells respond to the various colors.
(iii) As these cone-shaped cells respond only in bright light and not in faint light, we can sense colors only in bright light.

(c) We can not clearly see an object kept at a distance less than 25 cm from the eye.

Ans. (i) When we try to see a nearby placed object the eye lens adjusts by becoming more rounded and decreasing its focal length.
As a result we get a clear image of the object on the retina of the eye.
(ii) But the focal length of the eye cannot be decreased beyond a certain limit. Hence we cannot see an object kept at a distance less
than 25 cm from the eye.

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