Question

recombination of white light by 2 prisms

Answer 1

To get the light the original colour we place the two prisms inverted since one prism will diverge the light rays and the other inverted prism converge light rays to form the original light

here how it works the colours diverges due to the differences in wavelength

in the blue light divergence the most in the first prism is it is the least wavelength and the red light diverges the least from the top small part since it has a longer wavelength

now keeping the prism inverted we are incidenting the red wavelength into the thicker part which means the red light will bend more than the blue light which is incident on the thinner part of the second prism that is why the 7 rays convert again to form the original wavelength of light