$A$ thin prism $P_1$ with angle $4^{\circ}$ made of glass having refractive index $1.54$ is combined with another thin prism $P_2$ made of glass having refractive index $1.72$ to produce dispersion without deviation. The angle of the prism $P_2$ in degrees is:

At the condition of minimum deviation,the angle of emergence is .......

$A$ glass prism $A$ deviates the red and blue rays through $10^{\circ}$ and $12^{\circ}$ respectively. $A$ second prism $B$ deviates them through $8^{\circ}$ and $10^{\circ}$ respectively. The ratio of their dispersive powers is ($A$ to $B$):

$A$ ray of light is incident at an angle of $60^o$ on one face of a prism of angle $30^o$. The ray emerging out of the prism makes an angle of $30^o$ with the incident ray. The emergent ray is

The refractive index of the material of a prism is $\sqrt{2}$ and the angle of the prism is $30^{\circ}$. One of the two refracting surfaces of the prism is made a mirror inwards,by silver coating. $A$ beam of monochromatic light entering the prism from the other face will retrace its path (after reflection from the silvered surface) if its angle of incidence on the prism is (in $^{\circ}$)

For refraction through a small angled prism,the angle of deviation: