The image formed by a concave mirror is observed to be virtual,erect and larger than the object. Then the position of the object should be

Through which of the following points will a ray passing through the centre of curvature and reflected by a concave mirror pass?

As the velocity of light increases,the refractive index of the medium decreases. Light enters from air to water having a refractive index of $4/3$. Find the speed of light in water. The speed of light in vacuum is $3 \times 10^{8} \text{ m s}^{-1}$.

What can be measured using a dioptre meter?

$A$ student focussed the image of a candle flame on a white screen using a convex lens. He noted down the position of the candle,screen,and the lens as under:
Position of candle $= 12.0\, cm$
Position of convex lens $= 50.0\, cm$
Position of the screen $= 88.0\, cm$
$(i)$ Where will the image be formed if he shifts the candle towards the lens at a position of $31.0\, cm$?
$(ii)$ What will be the nature of the image formed if he further shifts the candle towards the lens?
$(iii)$ Draw a ray diagram to show the formation of the image in case $(ii)$ as said above.

Define the term power of a lens.