Light of wavelength 450nm is incident on a "diffraction grating" on which 5000 lines/cm have been ruled. Determine the angle corresponding to third order.
Correct answer: C. 42.5
- A. 13
- B. 26
- C. 42.5
- D. 39.5
Explanation
Wavelength = λ = 450 nm = 4.5 × 10-9mNo of lines = 5000/cmOrder of image = m= 3Grating element = d = 1/5000/cm = (1/5000)cmd = (1/500000) mAngle = θ =?d sinθ = mλsinθ = mλ / dθ = sin-1 mλ / dθ = sin-1 (3)(450 × 10-9) / (1/500000)mθ = sin-1 (3)(450 × 10-9m) (500000m-1)θ = sin-1 (0.675)θ = 42.5This is numerical so it can only have one answer so option C is correct.
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