A diffraction grating with 200 lines per mm is used in an experiment to study the visible spectrum of a gas discharge tube. At what angle from the beam axis will the first order peak occur if the tube emits light with wavelength of 617.3 nm

Answer

123.5 x 10 ^-3 radian

Explanation:

Given the Width of slit a = 1 x 10⁻³ / 200

a = 5x 10⁻⁶ m .

angle at which first order peak is formed

= λ / a (where λ is wavelength and a is width of slit)

given λ = 617.3 x 10⁻⁹ m

a = 5 x 10⁻⁶

θ = 617.3 x 10⁻⁹ / 5 x 10⁻⁶

= 123.5x 10⁻³ radian .

first order peak is formed at an angle of 123.5 x 10⁻³ radian .

Explanation:

real, smaller and upside-down.   so the answer should be b.