Ray Optics and Optical Instruments — Class 12 Physics PYQs

A beaker is filled with water (refractive index $\frac{4}{3}$) upto a height H. A coin is placed at its bottom. The depth of the coin, when viewed along the near normal direction, will be
(A) $\frac{H}{4}$
(B) $\frac{3H}{4}$
(C) H
(D) $\frac{4H}{3}$

The focal length of a concave mirror in air is f. When the mirror is immersed in a liquid of refractive index $\frac{5}{3}$, its focal length will become
(A) $\frac{5}{3}f$
(B) $\frac{3}{5}f$
(C) $\frac{2}{3}f$
(D) f

The plane face of a planoconvex lens is silvered. The refractive index of material and radius of curvature of the curved surface of the lens are n and R respectively. This lens will behave as a concave mirror of focal length
(A) $\frac{R}{n}$
(B) $\frac{R}{(n-1)}$
(C) nR
(D) $\frac{R}{2(n-1)}$

A transparent solid cylindrical rod (refractive index $\frac{2}{\sqrt{3}}$) is kept in air. A ray of light incident on its face travels along the surface of the rod, as shown in figure. Calculate the angle $\theta$.

Two concave lenses A and B, each of focal length 8.0 cm are arranged coaxially 16 cm apart as shown in figure. An object P is placed at a distance of 4.0 cm from A. Find the position and nature of the final image formed.

A double convex lens of glass has both faces of the same radius of curvature 17 cm. Find its focal length if it is immersed in water. The refractive indices of glass and water are 1.5 and 1.33 respectively.

When a parallel beam of light enters water surface obliquely at some angle, what is the effect on the width of the beam ?
(b) With the help of a ray diagram, show that a straw appears bent when it is partly dipped in water and explain it.
(c) Explain the transmission of optical signal through an optical fibre by a diagram.

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) The final image formed by the combination of lenses shown in figure is at a distance of
(A) 10 cm
(B) 20 cm
(C) 16 cm
(D) 22 cm
(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) A convex lens of focal length 'f' is cut into two equal parts perpendicular to the principal axis. The focal length of each part will be :
(A) f
(B) 2f
(C) f/2
(D) f/4
OR
(iii) If an object in case (i) above is 20 cm from the lens and the screen is 50 cm away from the object, the focal length of the lens used is
(A) 10 cm
(B) 12 cm
(C) 16 cm
(D) 20 cm
(iv) The distance of an object from first focal point of a biconvex lens is $X_1$ and distance of the image from second focal point is $X_2$. The focal length of the lens is
(A) $X_1{X}_2$
(B) $\sqrt{X_1+X_2}$
(C) $\sqrt{X_1{X}_2}$
(D) $\sqrt{X_2/X_1}$

Assertion (A) : The magnifying power of a compound microscope is negative.
Reason (R) : The final image formed is erect with respect to the object.

Assertion (A) : Plane and convex mirrors cannot produce real images under any circumstance.
Reason (R) : A virtual image cannot serve as an object to produce a real image.