CBSE Class 12 Physics 2023 Outside Delhi Set 1 Paper

Question : 33

Total: 35

(a) (i) State Huygen's principle. With the help of a diagram, show how a plane wave is reflected from a surface. Hence, verify the law of reflection.
(ii) A concave mirror of focal length 12‌cm forms a three times magnified virtual image of an object. Find the distance of the object from the mirror.
OR
(b) (i) Draw a labelled ray diagram showing the image formation by a refracting telescope. Define its magnifying power. Write two limitations of a refracting telescope over a reflecting telescope.
(ii) The focal lengths of the objective and the eyepiece of a compound microscope are 1.0‌cm and 2.5‌cm respectively. Find the tube length of the microscope for obtaining a magnification of 300.

Solution: 👈: Video Solution

(a) (i) Huygens' principle:
Each point on primary wavefront act as a source of secondary wavelets sending out disturbances in all directions in the similar manner as the original source of light does.
Verification of laws of reflection:
Refer the answer of Q26 (OR) of CBSE 12 DELHI, Set-1.
‌ (ii) ‌ ‌‌ Magnification ‌‌=−‌

‌‌ Or, ‌‌3‌=−‌

‌∴‌v‌=−3u
Applying mirror formula,
‌‌

+‌

=‌

‌‌ Or, ‌‌‌−‌

+‌

=−‌

‌‌ Or, ‌‌‌‌

u=−‌

‌∴‌‌u=−8‌cm
(b) (i) Refer the answer of Q33 (OR) (i) of CBSE 12 DELHI, Set-1.
Limitation of refracting telescope:
● Refracting telescope suffer from chromatic aberration.
● Large size Refracting telescopes are too heavy and too costly due to large size of lenses
(ii) Given,
f0‌=1‌cm
FE‌=2.5‌cm
m‌=300
‌ Since, ‌‌m‌=‌

L×D

f0×fE

‌ or, ‌‌300‌=‌

L×25

1×2.5

‌∴‌L‌=30‌cm

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