The radius of curvature of the curved surface of a plano-convex lens is 20 cm . If the refractive index of the material of the lens be 1.5 , it will

The phenomena involved in the reflection of radiowaves by ionosphere is similar to

The direction of ray of light incident on a concave mirror is shown by $P Q$ while directions in which the ray would travel after reflection is shown by four rays marked 1, 2, 3 and 4 (figure). Which of the four rays correctly shows the direction of reflected ray?

The optical density of turpentine is higher than that of water while its mass density is lower. Figure shows a layer of turpentine floating over water in a container. For which one of the four rays incident on turpentine in figure, the path shown is correct?

A car is moving with at a constant speed of $60 \mathrm{~km} \mathrm{~h}^{-1}$ on a straight road. Looking at the rear view mirror, the driver finds that the car following him is at a distance of 100 m and is approaching with a speed of $5 \mathrm{kmh}^{-1}$.

In order to keep track of the car in the rear, the driver begins to glance alternatively at the rear and side mirror of his car after every 2 s till the other car overtakes. If the two cars were maintaining their speeds, which of the following statement $(\mathrm{s})$ is/are correct?