Assertion: In Snell's law $\mu =\frac{\sin \left(i\right)}{\sin \left(r\right)}$, angle $i$ is always angle of incidence.

Reason: $\mu =\frac{\sin \left(i\right)}{\sin \left(r\right)}$ is applicable if the first medium is the air (or vacuum).

Assertion: Reflected image always travels in the opposite direction of object.

Reason: Speed of the point image formed by reflected rays is always equal to the speed of its point object.

Assertion: A ray of light travels from the first medium to a second medium. In the first medium angle of a ray with normal is $i_1=30°$ and in second medium $i_2=60°$ Then, the second medium is rarer medium.

Reason: Refractive index of the first medium with respect to the second medium is $\frac{\sin 30°}{\sin 60°}$.

Assertion: Focal length of a lens depends on the wavelength of light used.

Reason: The more the wavelengths, the lesser is the focal length.

Assertion: In front of a concave mirror a point object is placed between focus and centre of curvature. If a glass slab is placed between object and mirror, then an image from the mirror may become virtual.

Reason: Glass slab always makes a virtual image of a real object.

Assertion: Convex mirror will always make a virtual image.

Reason: Convex mirror is diverging in nature. Its power is negative.

Assertion: If angle of incidence in the case of a prism is gradually increased, then deviation produced by prism will first decrease then increase.

Reason: At minimum deviation, $r_1=\frac{A}{2}$.

Assertion: A mirror has only one focus, while that of less has two foci.

Reason: Both the foci of a mirror coincide at one point.

A transparent thin film of uniform thickness and refractive index $n_1=1.4$ is coated on the convex spherical surface of radius $R$ at one end of a long solid glass cylinder of refractive index $n_2=1.5$, as shown in the figure. Rays of light parallel to the axis of the cylinder traversing through the film from air to glass get focused at distance $f_1$ from the film, while rays of light traversing from glass to air get focused at distance $f_2$ from the film. Then,