Tricky questions

## Ray Optics And Optical Instruments

- Some questions are often misinterpreted by the students. Let's explore them!
1
Many times, we often tend to substitute the relative refractive index values incorrectly in the lens maker's formula. Let's solve this question to understand it better.
2
For refraction at spherical interface, there is a high possibility that we substitute the values of radius of curvature with incorrect sign. This leads to a wrong answer for the image position.
3
In questions involving combination of lenses and mirrors, there can be a mistake while applying sign convention. Note that the direction of light is always taken to be positive. After reflection from a mirror, we will have to reverse the sign convention for the subsequent refractions and/or reflections.
4
While tracing the path of ray being refracted by a prism, we often forget to consider the case of total internal reflection. So it is advised to always check the critical angle for dense-to-rare medium refraction. If the angle of incidence is more than critical angle, then the incident ray will be reflected back in the prism's medium.
5
In questions about telescopes, we have to read the question very carefully. We might make a mistake in deriving or applying the formula of magnifying power. We have to check whether the magnifying power for image formed least distance of distinct vision is asked, or magnifying power image formed at infinity is asked.