Refractive index of diamond with respect to glass is $1.6$ and absolute refractive index of glass is $1.5$. Find out the absolute refractive index of diamond.

When is the magnitude of the power of a lens equal to its focal length?

$(a)$ State the relation between object distance,image distance and the focal length of a spherical mirror.
$(b)$ Draw a ray diagram to show the image formed by a concave mirror when an object is placed between the pole and focus of the mirror.
$(c)$ $A$ concave mirror of focal length $15\, cm$ forms an image of an object kept at a distance of $10\, cm$ from the mirror. Find the position,nature and size of the image formed by it.

What is the distance between the pole and the principal focus of a spherical mirror called?

Write two important applications of $(i)$ concave mirror and $(ii)$ convex mirror.

For the same angle of incidence in media $P, Q$ and $R$,the angles of refraction are $45^{\circ}, 35^{\circ}$ and $15^{\circ}$ respectively. In which medium will the velocity of light be minimum? Give reason.