Rankers Physics

Reflection by Spherical Mirrors: Practice Problem & Solution

A concave mirror of focal length $f_1$ is placed at a distance of d from a convex lens of focal length $f_2$ . A beam of light coming from infinity and falling on this convex lens-concave mirror combination returns to infinity. The distance 'd' must equal: (2012 Pre)
$-2f_1 + f_2$
$f_1 + f_2$
$-f_1 + f_2$
$2f_1 + f_2$

Short Solution (Best for NEET):

To solve this problem, we apply the core principles of Reflection by Spherical Mirrors. Understanding the underlying formula is key to arriving at the correct answer below:

Light from infinity passes through the convex lens and converges at its principal focus, a distance $f_2$ from the lens. For the light to return to infinity, it must retrace its path after reflection from the concave mirror. This happens if the rays strike the mirror normally, meaning they appear to come from the mirror's center of curvature (at distance $2f_1$ ). So, $d = 2f_1 + f_2$ .

Leave a Reply

Your email address will not be published. Required fields are marked *

Similar Practice Questions

Explore conceptually related problems to test your knowledge.

1. If a container of height \(17.3\text{ cm}\) is filled with a liquid of refractive index \(\mu\). The bottom of container appear to be raised by \(3.46\text{ cm}\) when seen from above. Refractive index of liquid is
2. For a normal eye, the cornea of eye provides a converging power of 40 D and the least converging power of the eye lens behind the cornea is 20 D. Using this information, the distance between the retina and the cornea of eye lens can be estimated to be: (2013)
3. Light travels through a glass plate of thickness t and having a refractive index $\mu$. If c is the velocity of light in vacuum, the time taken by light to travel this thickness of glass is (1996)
4. Match the corresponding entries of column-1 with column-2. [where m is the magnification produced by the mirror] \begin{array}{ll} \textbf{Column-I} & \textbf{Column-II} \\[1ex] \text{(A) } m = -2 & \text{(1) Convex mirror} \\ \text{(B) } m = -\frac{1}{2} & \text{(2) Concave mirror} \\ \text{(C) } m = +2 & \text{(3) Real image} \\ \text{(D) } m = +\sqrt{\frac{2}{3}} & \text{(4) Virtual image} \end{array} (2016 - I)
5. Optical fibre are based on: (2001)