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CAIE A-Level Physics 8.4.1 Using d sin θ = nλ

Practise using d sin theta = n lambda to calculate grating angle, wavelength or order, rearranging with spacing or line density and checking allowed maxima.

Syllabus
2028–2030
Course
Physics 9702
Level
AS

Exam points

  • calculate wavelength, diffraction order or angle using d sin θ = nλ
  • rearrange d sin θ = nλ and use grating spacing or line density consistently
  • interpret diffraction-grating maxima and check the allowed order or angle

8.4.1—D sin θ = nλ question 1

[Maximum number: 6]

Question (a)

(a)

A diffraction grating is used to determine the wavelength of light.

[ 3 ]

Question (i)

(i)

By reference to interference, explain

[ 3 ]

Question (i)

(i)

1. the zero order maximum,

Question (ii)

(ii)

2. the first order maximum.

[ 3 ]

Question (b)

(b)

A diffraction grating is used with different wavelengths of light. The angle θ\theta of the second order maximum is measured for each wavelength. The variation with wavelength λ\lambda of sin⁡θ\sin \theta is shown in Fig. 5.1.

Fig. 5.1

Fig. 5.1

[ 3 ]

Question (i)

(i)

Use the gradient determined in (i) to calculate the slit separation d of the diffraction grating.

d=
[ 2 ]

Question (ii)

(ii)

On Fig. 5.1, sketch a line to show the results that would be obtained for the first order maxima.

[ 1 ]
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