Optics MCQs for NEET — Physics Questions with Answers

The NCERT text mentions: 'We have already studied that the geometric centre of a spherical mirror is called its pole...'

The NCERT text describes paraxial rays as: 'We assume that the rays are paraxial, i.e., they are incident at points close to the pole P of the mirror and make small angles with the principal axis.'

The NCERT text clearly states: 'With the proper use of sign convention, these are, in fact, valid for all the cases of reflection by a spherical mirror (concave or convex) whether the image formed is real or virtual.'

The NCERT text mentions: 'If the parallel paraxial beam of light were incident, making some angle with the principal axis, the reflected rays would converge (or appear to diverge) from a point in a plane through F normal to the principal axis. This is called the focal plane of the mirror [Fig. 9.3(c)].'

According to the Cartesian Sign Convention summary provided: 'The heights measured upwards above x-axis and normal to the principal axis of the mirror/lens are taken as positive. The heights measured downwards are taken as negative.'

The NCERT text states this as a rule for ray tracing: 'The ray passing through the centre of curvature of a concave mirror or appearing to pass through it for a convex mirror. The reflected ray simply retraces the path.'

The NCERT text defines a virtual image as: 'The image is real if the rays actually converge to the point; it is virtual if the rays do not actually meet but appear to diverge from the point when produced backwards.'

According to the NCERT text, 'When light travels from an optically denser medium to a rarer medium at the interface, it is partly reflected back into the same medium and partly refracted to the second medium. This reflection is called the internal reflection.' For total internal reflection, light must travel from a denser to a rarer medium, and the angle of incidence must exceed the critical angle.

The NCERT text states, 'For values of i larger than ic, Snell’s law of refraction cannot be satisfied, and hence no refraction is possible.' In this case, 'the incident ray is totally reflected. This is called total internal reflection.'

The NCERT summary lists 'Multiple internal reflections in diamond ($i_c \approx 24.4^\circ$), totally reflecting prisms and mirage, are some examples of total internal reflection.' Optical fibres are also stated to make use of total internal reflection. Rainbow formation primarily involves dispersion and refraction, not total internal reflection in its primary mechanism.