| Date | November 2015 | Marks available | 2 | Reference code | 15N.3.SL.TZ0.3 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 0 |
| Command term | Calculate | Question number | 3 | Adapted from | N/A |
Question
This question is about diffraction and resolution.
Monochromatic light is incident normally on a single narrow slit and gives rise to a diffraction pattern on a screen.
Sketch, for the diffraction pattern produced, a graph showing the variation of the relative intensity of the light with the angle measured from the centre of the slit.
The single narrow slit is replaced by a double narrow slit. Explain, with reference to your answer to (a), how the Rayleigh criterion applies to the diffraction patterns produced by the light emerging from the two slits.
Two lamps emit light of wavelength 620 nm. The lights are observed through a circular aperture of diameter 1.5 mm from a distance of 850 m. Calculate the minimum distance between the lamps so that they are resolved.
Markscheme
large central peak and at least one subsidiary maximum on each side;
minima have intensity of zero and intensity of secondary maxima at most 25 % of central maximum; } (judge by eye)
explanation of resolving – seeing images as being from separate objects;
idea of diffraction patterns overlapping;
central maximum being at least as far from companion as the first minimum;
Marking points may be seen on graph in (a).
Marking points may be seen from diffraction pattern showing resultant intensity from two sources with a slight dip in the centre.
equating \(1.22\frac{\lambda }{b}\) to \(\frac{x}{D}\);
0.43 (m);
Examiners report
The majority could correctly sketch the diffraction pattern and only a few showed non-zero intensity at the minima. The definition of Rayleigh’s criterion was well known but candidates found it difficult to gain full marks explaining how the Rayleigh criterion applies to diffraction patterns, as asked. The calculation was well-attempted.
The majority could correctly sketch the diffraction pattern and only a few showed non-zero intensity at the minima. The definition of Rayleigh’s criterion was well known but candidates found it difficult to gain full marks explaining how the Rayleigh criterion applies to diffraction patterns, as asked. The calculation was well-attempted.
The majority could correctly sketch the diffraction pattern and only a few showed non-zero intensity at the minima. The definition of Rayleigh’s criterion was well known but candidates found it difficult to gain full marks explaining how the Rayleigh criterion applies to diffraction patterns, as asked. The calculation was well-attempted.
