3.3.2.2
Single slit diffraction has a wide, bright central maximum
Interference & Diffraction — AQA A-Level Physics
- The central maximum is much wider and brighter than the side maxima.
- Side maxima decrease in intensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared. with increasing distance from the centre.
- Dark fringes (minima) have zero intensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared..
- This pattern is distinctly different from the double slit pattern (which has equally spaced, equally bright fringes).
Effect of changing wavelengthThe minimum distance between two points on a wave that are in phase (e.g. crest to crest). Measured in metres (m). or slit width
- Increasing wavelengthThe minimum distance between two points on a wave that are in phase (e.g. crest to crest). Measured in metres (m). (e.g. red instead of blue): fringes become wider, more diffraction occurs.
- Decreasing slit width: central maximum becomes wider, intensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared. decreases, greater angle of diffraction.
- Increasing slit width: central maximum becomes narrower, less diffraction.
White light through a single slit
- Central maximum is bright white (all wavelengths constructively interfere).
- Other maxima show a spectrum: violet/blue closest to the centre, red furthest out.
- Spectra blur and merge further from the centre.