Reflection of Light — NEET Physics PYQ MCQs with Solutions

Solution: Object distance, $u = -1.5f$ By mirror formula, $\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$ $\frac{1}{v} + \frac{1}{-1.5f} = \frac{1}{-f}$ $\frac{1}{v} = -\frac{1}{f} + \frac{1}{1.5f} = -\frac{1}{f}\left(1 - \frac{2}{3}\right) = -\frac{1}{3f}$ $\Rightarrow v = -3f$

Solution: Key Concept: The net displacement of the image equals the difference between the image distances in the two cases. Case 1: $u_1 = -40$ cm, $f = -15$ cm $\frac{1}{f} = \frac{1}{v_1} + \frac{1}{u_1}$ gives $\frac{1}{v_1} = -\frac{1}{15} + \frac{1}{40} = \frac{-5}{120}$, so $v_1 = -24$ cm Case 2: $u_2 = -20$ cm $\frac{1}{v_2} = -\frac{1}{15} + \frac{1}{20} = \frac{-1}{60}$, so $v_2 = -60$ cm Displacement of image $= v_2 - v_1 = -60 - (-24) = -36$ cm $= 36$ cm, away from the mirror.

Solution: When light is incident normally on a plane mirror, it is reflected back along the same path. When the mirror is rotated by a small angle $\theta$, the reflected ray rotates by $2\theta$. The spot moves a distance y on a scale at distance x, so $2\theta = \frac{y}{x}$ $\Rightarrow \theta = \frac{y}{2x}$

Solution: A negative magnification means a real, inverted image — formed only by a concave mirror. So $m = -2$ and $m = -\frac{1}{2}$ both correspond to a concave mirror forming a real image (b and c). A positive magnification means a virtual, erect image. $m = +2$ (magnified virtual image) is formed by a concave mirror with the object between pole and focus (b and d). $m = +\frac{1}{2}$ (diminished virtual image) is formed by a convex mirror (a and d).

Solution: A parallel beam from infinity converges at the focus of the convex lens, at distance $f_2$ from the lens. For the beam to return to infinity after reflection, the rays must retrace their path — so this focus must coincide with the centre of curvature of the concave mirror, which lies at distance $2f_1$ from the mirror. Hence $d = 2f_1 + f_2$.

Solution: The minimum size of a plane mirror required to see the full image of a person $= \frac{\text{height of person}}{2} = \frac{6}{2} = 3$ ft

Solution: When an object is held between two plane mirrors inclined at angle $\theta$, multiple reflections form several images. The total number of images is $n = \frac{360°}{\theta} - 1$ Here $\theta = 60°$, so $n = \frac{360°}{60°} - 1 = 6 - 1 = 5$

Solution: Ray optics uses the geometry of straight lines to account for macroscopic phenomena like rectilinear propagation, reflection and refraction. It is the limiting case of wave optics, valid when the dimensions involved are much larger than the wavelength of light.