Read the following and answer any four questions from 19 (i) to 19 (v)
Sumati wanted to see the stars of the night sky. She knows that she
needs a telescope to see those distant stars. She finds out that the
telescopes, which are made of lenses, are called refracting telescopes
and the ones which are made of mirrors are called reflecting telescopes.
So she decided to make a refracting telescope. She bought two lenses,
L1 and L2. out of which L1 was bigger and L2 was smaller. The larger
lens gathers and bends the light, while the smaller lens magnifies the
image. Big, thick lenses are more powerful. So to see far away, she
needed a big powerful lens. Unfortunately, she realized that a big lens is
very heavy. Heavy lenses are hard to make and difficult to hold in the
right place. Also since the light is passing through the lens, the surface of
the lens has to be extremely smooth. Any flaws in the lens will change the
image. It would be like looking through a dirty window.
1x4
(i) Based on the diagram shown, what kind of lenses would Sumati need
to make the telescope?
a) Concave lenses b) Convex lenses
c) Bifocal lenses d) Flat lenses
(ii) If the powers of the lenses L1 and L2 are in the ratio of 4:1, what
would be the ratio of the focal length of L1 and L2?
a) 4:1 b) 1:4
c) 2:1 d) 1:1
1
(iii) What is the formula for magnification obtained with a lens?
a) Ratio of height of image to height of object
b) Double the focal length.
c) Inverse of the radius of curvature.
d) Inverse of the object distance.
1
(iv) Sumati did some preliminary experiment with the lenses and found
out that the magnification of the eyepiece (L2) is 3. If in her experiment
with L2 she found an image at 24 cm from the lens, at what distance did
she put the object?
a) 72 cm b) 12 cm
c) 8 cm d) 6 cm
1
(v) Sumati bought not-so-thick lenses for the telescope and polished
them. What advantages, if any, would she have with her choice of
lenses?
a) She will not have any advantage as even thicker lenses would give
clearer images.
b) Thicker lenses would have made the telescope easier to handle.
c) Not-so-thick lenses would not make the telescope very heavy and also
allow considerable amount of light to pass.
d) Not-so-thick lenses will give her more magnification.
Answers
Answer:
(a) convex lens
(b) 1:4
(c) ratio of height of to height of imat
(d) 72cm
(e) not so thick will be giver megnification
Answer:
(a) convex lens
(b) 1:4
(c) ratio of height of to height of inmate
(d) 72cm
(e) not so thick will be giver magnification
Explanation:
Step:1 Two spherical surfaces often make up an optical lens. The lens is referred to as a biconvex lens or just a convex lens if those surfaces are curved outwards. These lenses have the ability to focus an outside light beam to a spot on the opposite side by converging it.
Convex lenses are used in eyeglasses to treat farsightedness, a condition where the retina and lens of the eye are too close together and the focal point is behind the retina. Convex lenses on eyeglasses increase refraction and hence shorten the focal length.
Step :2 It describes the process of using lenses to enlarge an object visually. Additionally, the thing simply appears larger and does not actually become bigger. Additionally, this idea comes from two different forms.
First, use a microscope to magnify small things, and then a telescope (that makes a distant object appear closer and the images are more clear and defined).
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