The property of light used in optical fibre cables is
Two plane mirrors A and B are aligned parallel to each other as shown in the figure.
A ray of light is incident at an angle 30$$^\circ$$ at a point just inside one end of A. The plane of incidence coincides with the plane of the figure. The maximum number of times, the ray undergoes reflection (excluding the first one) before it emerges out is
A thin equi-convex lens is made of glass of refractive index 1.5 and its focal length is 0.2 m. If it acts as a concave lens of focal length 0.5 cm when dipped in a liquid, the refractive index of the liquid is
A spherical lens of power $$-$$4D is placed at a distance of 15 cm from another spherical lens of power 5 D. A beam of parallel light falls on the first spherical lens. The final image formed is