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Science · 2025 · 5 marks
CBSE 2025 · Region 1 · Set 1 · Q36
(a) (i) The power of a lens 'X' is -2•5 D. Name the lens and determine its focal length in cm. For which eye defect of vision will an optician…
(i)
The power of a lens 'X' is -$\displaystyle 2$•$\displaystyle 5$ D. Name the lens and determine its focal length in cm. For which eye defect of vision will an optician prescribe this type of lens as a corrective lens?
(ii)
"The value of magnification 'm' for a lens is -2." Using new Cartesian Sign Convention and considering that an object is placed at a distance of $\displaystyle 20$ cm from the optical centre of this lens, state :
(I)
the nature of the image formed;
(II)
size of the image compared to the size of the object;
(III)
position of the image, and
(IV)
sign of the height of the image.
(iii)
The numerical values of the focal lengths of two lenses A and B are $\displaystyle 10$ cm and $\displaystyle 20$ cm respectively. Which one of the two will show higher degree of convergence/divergence ? Give reason to justify your answer.
(i)
Draw a ray diagram to show the refraction of a ray of light through a rectangular glass slab when it falls obliquely from air into glass.
(ii)
State Snell's law of refraction of light.
(iii)
Differentiate between the virtual images formed by a convex lens and a concave lens on the basis of:
(I)
object distance, and
(II)
magnification.
Marking-scheme solution
\(\displaystyle \frac{1}{2} \times 4\)
(b) (i)
(ii)
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 a given pair of media. /
\[\frac{\sin i}{\sin r}=\text { constant }
\]
(iii)
| Convex Lens | Concave Lens |
| (I) Object to be placed between O and F | Object can be placed anywhere in front of the lens |
| (II) Magnified image | Diminished image |
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CBSE Class 10 Science past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.