a diffraction grating is illuminated with yellow light at normal incidence. The

Question

a diffraction grating is illuminated with yellow light at normal incidence. The pattern seen on a screen behind the grating consists of three yellow spots, one at zero degrees (straight through) and one each at +/- 45 degrees. You now add red light of equal intensity, coming in the same direction as the yellow lightTher new apttern consisits of

1. red spots at 0 and +/- 45

2. yellow spots at 0 and +/- 45

3. Orange spots at 0 and +/- 45

4. an orange spot at 0, yellow spots at +/- 45, and red spots slightly further out

5. an orange spot at 0, yellow spots at +/- 45, and red spots slightly closer in

Explanation / Answer

In this case, the new pattern consists of orange spot [red + yellow] at 0o because

there is always a centeral maximum for each wavelength of lght. The seperation

distance between the peaks of the subsequent maxima varies directly with the wavelength

of the light. Hence, the red spots are slightly further out than the yellow spots.

Therefore, option (4) is correct.

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