In a diffraction grating, what does m represent in the equation d sin θ = m λ?

In a diffraction grating, what does m represent in the equation d sin θ = m λ?

• A. Wavefront index
• B. Grating spacing
• C. Integer order of the diffraction maximum
• D. Angle of diffraction

Answer: (C)

m is the integer order of the diffraction maximum. When light from many slits in a grating interferes, a bright fringe occurs only when the extra distance light travels from adjacent slits equals an integer multiple of the wavelength, so the waves arrive in phase: d sin θ = m λ. The central bright spot is the zero order (m = 0), with first-order maxima at m = ±1, then ±2, and so on. Only integer values of m produce perfectly constructive interference across all slits, which is why they label the bright fringes.

m is the integer order of the diffraction maximum. When light from many slits in a grating interferes, a bright fringe occurs only when the extra distance light travels from adjacent slits equals an integer multiple of the wavelength, so the waves arrive in phase: d sin θ = m λ. The central bright spot is the zero order (m = 0), with first-order maxima at m = ±1, then ±2, and so on. Only integer values of m produce perfectly constructive interference across all slits, which is why they label the bright fringes.