CBSE 2025 · Region 1 · Set 1 · Q30 · 4 marks

A thin lens is a transparent optical medium bounded by two surfaces, at least one of which should be spherical. Applying the formula for image formation by a single spherical surface successively at the two surfaces of a lens, one can obtain the 'lens maker formula' and then the 'lens formula'. A lens has two foci - called 'first focal point' and 'second focal point' of the lens, one on each side. $$

(i)

(i)

Consider the arrangement shown in figure. A black vertical arrow and a horizontal thick line with a ball are painted on a glass plate. It serves as the object. When the plate is illuminated, its real image is formed on the screen. Which of the following correctly represents the image formed on the screen?

(i)

(A)

(B)

(C)

(D)

(ii)

Which of the following statements is incorrect?

(A)

For a convex mirror magnification is always negative.

(B)

For all virtual images formed by a mirror magnification is positive.

(C)

For a concave lens magnification is always positive.

(D)

For real and inverted images, magnification is always negative.

(iii)OR(iii)

A convex lens of focal length'$\displaystyle \mathrm{f}$'is cut into two equal parts perpendicular to the principal axis. The focal length of each part will be:

(A)

f (B) $\displaystyle 2$ f

(C)

$\displaystyle \frac{\mathrm{f}}{2}$

(D)

$\displaystyle \frac{\mathrm{f}}{4}$

(iv)

The distance of an object from first focal point of a biconvex lens is $\displaystyle \mathrm{X}_{1}$ and distance of the image from second focal point is $\displaystyle \mathrm{X}_{2}$. The focal length of the lens is

(A)

$\displaystyle \mathrm{X}_{1} \mathrm{X}_{2}$

(B)

$\displaystyle \sqrt{\mathrm{X}_{1}+\mathrm{X}_{2}}$

(C)

$\displaystyle \sqrt{\mathrm{X}_{1} \mathrm{X}_{2}}$

(D)

$\displaystyle \sqrt{\frac{\mathrm{X}_{2}}{\mathrm{X}_{1}}}$

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CBSE Class 12 Physics past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.