3.3.2.2
A diffraction grating produces sharp, bright maxima
Interference & Diffraction — AQA A-Level Physics
- A diffraction gratingAn optical component with many equally spaced parallel slits that produces sharp interference maxima at specific angles. has many equally spaced parallel slits (typically hundreds per mm).
- It produces the same pattern as a double slit but with much sharper, brighter maxima and wider dark regions.
- This makes it much more useful for precise wavelengthThe minimum distance between two points on a wave that are in phase (e.g. crest to crest). Measured in metres (m). measurement.
$$d \sin \theta = n\lambda$$
- $d$: slit spacing (m)
- $\theta$: angle of diffraction from the normal (degrees)
- $n$: order of the maximum (0, 1, 2, 3...)
- $\lambda$: wavelengthThe minimum distance between two points on a wave that are in phase (e.g. crest to crest). Measured in metres (m). (m)
- The slit spacing d is calculated from the number of slits per metre N:
$$d = \frac{1}{N}$$
- $d$: slit spacing (m)
- $N$: number of slits per metre (\(m^{-1}\))
- If N is given in lines per mm, convert to lines per m before calculating d.
- The zero-order maximum ($n = 0)$ is the central, undeviated beam at $\theta = 0$.
- Higher orders appear at greater angles from the centre.