Monochromatic light of wavelength $5.8 imes 10^{-7} ext{ m}$ is incident normally on a plane transmission diffraction grating that has a slit separation of $2.5 imes 10^{-6} ext{ m}$ - AQA - A-Level Physics - Question 21 - 2022 - Paper 1

To find the number of maxima produced by the grating, we use the formula for the diffraction condition:

$d imes ext{sin}( heta) = m imes ext{wavelength}$

where:

• $d$ is the slit separation, which is $2.5 imes 10^{-6} ext{ m}$,
• $m$ is the order of the maximum,
• $ext{wavelength}$ is $5.8 imes 10^{-7} ext{ m}$.

The maximum order $m$ is found when $ext{sin}( heta) = 1$, therefore:

m_{max} = rac{d}{ ext{wavelength}}

Substituting the known values:

m_{max} = rac{2.5 imes 10^{-6}}{5.8 imes 10^{-7}} \\ m_{max} \\approx 4.31

Since $m$ must be an integer, the maximum order of diffraction is 4.