Question

which will be preferred large angle prism or small angle prism for obtaining spectrum? Why?

Answer 1

$\bold{\text{very nice question}}$
$\bold{\text{for my point of view we should prefer large angle prism for obtaining spectrum.}}$

if you know, about angle of deviation, then you should remind the relation between deviation angle and angle of prism ,
$e.g., \delta=(\mu-1)A$
hence, deviation angle will be maximum when angle of prism will be maximum. hence, if we choose the prism of small angle , then angle of incidence ray is almost perpendicular to the plane of incidence. obviously , the angle of deviation will be very small. it's hard to count the width of each region of colors .

but when we choose the prism of large angle, deviation angle will be high . then, width of region of colors will be large , so, it's easy to obtain the spectrum.

hence, in simple way , we choose large angle prism due to obtain better spectrum.

Answer 2

It ought to be a prism with a large angle. This is on account of, in the event of a thin prism, the point of the prism is extremely little, most likely lesser than 15° even with the goal that the incident ray is relatively opposite to the plane of frequency.

Presently, for the light going through the crystal, to experience diffusing, it is a prime prerequisite for the light rays to movement some distance in that Refractive material of the crystal, so that, contingent on the distinction in paces of various shades of white light, there could be sufficient separation made a trip by each shading to experience the ill effects of a calculable degree of deviation from its nearest color, and winds up plainly recognizable at the photographic plate.