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Science · 2023 · 5 marks
CBSE 2023 · Region 2 · Set 1 · Q36
(a) An object is placed in front of a convex lens of focal length f. If the distance of the object from the lens is 2f, draw a ray diagram to show…
(a)
An object is placed in front of a convex lens of focal length f. If the distance of the object from the lens is 2f, draw a ray diagram to show the formation of the image. Write the value of magnification in this case.
(b)
A student has focussed the image of a candle flame on a white screen using a convex lens. The situation is as given below : Length of the flame = $\displaystyle 2$ cm Focal length of the lens = $\displaystyle 12$ cm Distance of the flame from the lens $\displaystyle =16 \mathrm{~cm}$ If the flame is perpendicular to the principal axis of the lens, calculate the values of the following :
(i)
Distance of the image from the lens
(ii)
Length of the image formed
Marking-scheme solution
(a) •
Magnification = -$\displaystyle 1$
(b) (i) \(\displaystyle \mathrm{u}=-16 \mathrm{~cm} ; \mathrm{f}:+12 \mathrm{~cm}\)
Formula \(\displaystyle \frac{1}{\mathrm{v}}-\frac{1}{\mathrm{u}}=\frac{1}{\mathrm{f}}\)
Substitution Result \(\displaystyle \frac{1}{\mathrm{v}}=\frac{1}{\mathrm{u}}+\frac{1}{\mathrm{f}}=\frac{1}{-16 \mathrm{~cm}}+\frac{1}{12 \mathrm{~cm}}+\frac{+1}{48 \mathrm{~cm}}\) or \(\displaystyle \mathrm{V}=+48 \mathrm{~cm}\) or \(\displaystyle \mathrm{v}=+48 \mathrm{~cm}\) (iv) \(\displaystyle \mathbf{h i}=\frac{\mathrm{v}}{\mathrm{u}} \times \mathrm{h}_{0} =\frac{+48 \mathrm{~cm}}{-16 \mathrm{~cm}} \times 2 \mathrm{~cm} =-\mathbf{6 ~ c m}\) Image is $\displaystyle 6$ cm in size.
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CBSE Class 10 Science past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.