Question

When white light passes through the achromatic combination of prisms, then what is observed

• A. Only deviation
• B. Only dispersion
• C. Deviation and dispersion
• D. None of the above

Answer 1

Answer: (A)

Only deviation

When white light passes through a prism , it disperses into band of seven colours. But when two prism are combined in such a way that sum of angular dispersions of crown glass prism and flint glass prism is zero then such a combination is achromatic combination of prisms. When white light passes through achromatic combination of prisms, internally dispersed components of white light from Crown glass prism refract and meet together at the outer surface edge of Flint Glass prism ,so the refracted light from the achromatic combination of prisms become white light again with deviation only without any dispersion.