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Science · 2024 · 5 marks
CBSE 2024 · Region 4 · Set 3 · Q36
(i)State laws of reflection of light.(ii)An object of height $\displaystyle 5$⋅$\displaystyle 0$ cm is placed at $\displaystyle 15$ cm in front of a concave mirror of focal length $\displaystyle 10$ cm. At what distance from the mirror should a screen be placed, so that a focussed image is obtained on it ? Find the height of the image.(i)State laws of refraction of light.(ii)Draw a ray diagram to show refraction of a ray of light through a rectangular glass slab. How is the emergent ray related to incident ray ? Mark lateral displacement in the diagram.
(i)
State laws of reflection of light.
(ii)
An object of height $\displaystyle 5$⋅$\displaystyle 0$ cm is placed at $\displaystyle 15$ cm in front of a concave mirror of focal length $\displaystyle 10$ cm. At what distance from the mirror should a screen be placed, so that a focussed image is obtained on it ? Find the height of the image.
(i)
State laws of refraction of light.
(ii)
Draw a ray diagram to show refraction of a ray of light through a rectangular glass slab. How is the emergent ray related to incident ray ? Mark lateral displacement in the diagram.
Marking-scheme solution
(a) (i)
The angle of incidence is equal to the angle of reflection.
The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.
(ii) \(\displaystyle \mathrm{u}=-15 \mathrm{~cm}, \mathrm{f}=-10 \mathrm{~cm}\) (concave mirror)
\[h=5.0 \mathrm{~cm}
\]
Mirror formula \(\displaystyle \frac{1}{f}=\frac{1}{v}+\frac{1}{u}\)
\[\frac{1}{v}=\frac{-1}{10 \mathrm{~cm}}+\frac{1}{15 \mathrm{~cm}}=\frac{-1}{30 c m}
\]
or \(\displaystyle \mathrm{v}=-30 \mathrm{~cm}\). The screen must be placed at a distance of $\displaystyle 30$ cm from the mirror in front of it
\(\displaystyle (m)=\frac{h^{\prime}}{h}=-\frac{v}{u}\)
\(\displaystyle \bar{h}=\frac{-\bar{v}}{u} \times \bar{h}=-\frac{-30 c m}{-15 c m} \times 5 c m=-10 \mathrm{~cm}\)
OR
(b)(i)-The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.
The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given colour and for the given pair of media. /
\[\frac{\sin i}{\sin r}=\text { constant }
\]
The emergent ray is parallel to the incident ray.
Labelling of lateral displacement
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CBSE Class 10 Science past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.