Question

In producing a pure spectrum, the incident light is passed through a narrow slit placed in the focal plane of an achromatic lens because a narrow slit ___________ .

Options

• produces less diffraction

• increases intensity

• allows only one colour at a time

• allows a more parallel beam when it passes through the lens

Answer 1

allows a more parallel beam when it passes through the lens

 

To produce a pure spectrum, a parallel light beam is required to be incident on the dispersing element. So, the incident light is passed through a narrow slit placed in the focal plane of an achromatic lens.