Question 22N.2.HL.TZ0.7
| Date | November 2022 | Marks available | [Maximum mark: 11] | Reference code | 22N.2.HL.TZ0.7 |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Calculate, Comment, Explain, Outline, Sketch | Question number | 7 | Adapted from | N/A |
A beam of coherent monochromatic light is incident normally on a single rectangular slit. The diffraction pattern is observed on a screen.
O is the point on the screen directly opposite the slit. P and Q are the first minima on either side of the central fringe of the diffraction pattern.
The intensity of light at point O is . The distance OP is .
Sketch, on the axes, a graph to show the variation of the intensity of light with distance from point O on the screen. Your graph should cover the distance range from 0 to 2.
[2]
smooth curve decreasing from to 0 between 0 and ✓
secondary maximum correctly placed AND of intensity less than 0.3 ✓
E.g. 
Most scored MP1. Many candidates scored full marks but it was common to see a maximum at 2x or a secondary maxima too high.
Early theories of light suggest that a geometrical shadow of the slit will be observed on the screen. Explain how the diffraction pattern formed on the screen provides evidence for the wave theory of light.
[2]
observed pattern goes beyond the rectangular shape/geometrical shadow
OR
observed pattern shows maxima/minima ✓
«this is explained by» interference/superposition of waves ✓
Accept any correct description of the diffraction pattern for MP1.
Well answered. Most candidates scored a mark with specific reference to interference/superposition of waves although some missed a clear reference to a detail of the diffraction pattern or a reference of the discrepancy between this pattern and the geometrical shadow expected.
The following data are available.
Wavelength of light = 590 nm
Distance between the slit and the screen = 2.4 m
Width of the slit = 0.10 mm
Calculate distance PQ.
[2]
angle of the first minimum « rad» ✓
width «m» ✓
1.4 × 10−2 m scores [1] mark.
Do not penalize the use of sin or tan in MP2.
Well answered.
The single slit is replaced by a double slit. The width of each slit in this arrangement is the same as the width of the single slit in (a).
Outline how the intensity variation observed between points P and Q will change.
[2]
intensity at O increases ✓
fringes / a series of maxima and minima ✓
with intensity decreasing away from O
OR
intensity modulated by diffraction ✓
Accept answers as sketches. For MP1 expect the scale on the y-axis.
E.g.
The most successful answers were accompanied by a diagram. It is worthy to emphasize that the presence of a blank space within the box should be taken as an indicator of the convenience of using sketches to complete the answer or communicate the ideas more easily. It was often easy to award 2 marks from the diagram, even though the new peak intensity usually was not labelled.
The light source actually emits two wavelengths of light. The average wavelength is 590 nm and the difference between the two wavelengths is 0.60 nm.
A student attempts to resolve the wavelengths using a diffraction grating with 750 lines per mm. The incident beam is 2.0 mm wide.
Comment on whether this diffraction grating can resolve the wavelengths in the first-order spectrum.
[3]
ALTERNATIVE 1
number of illuminated slits ✓
smallest resolvable difference «» «nm» ✓
hence the lines can be resolved ✓
ALTERNATIVE 2
number of illuminated slits ✓
✓
greater than hence lines can be resolved ✓
Allow ECF from MP2.
Many answers showed confusion about the meaning of the equation in the data booklet. There were some wrong conclusions that compared the two numbers, and not being equal, concluded that the lines could not be resolved. Strongest candidates scored full marks easily.