Both a spherical mirror and a thin spherical lens have a focal length of $-15 \; cm$. What type of mirror and lens are they?

The formation of an image by a lens is due to which optical phenomenon?

Which of the following always form a virtual image?

$(a)$ 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.

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.

The laws of reflection are true only for plane mirrors and not for curved mirrors.