Checkpoint 2 assesses L03, L04, L05, L10 in the published syllabus sequence.
Assessment is drawn only from this lesson’s repaired effective pool.
Assessment is drawn only from this lesson’s repaired effective pool.
Assessment is drawn only from this lesson’s repaired effective pool.
Assessment is drawn only from this lesson’s repaired effective pool.
This checkpoint assesses L03, L04, L05, L10 only. Lesson file IDs remain stable; displayed lesson numbers follow the module’s syllabus sequence.
1. In Young's double slit experiment, a dark fringe appears at a point on the screen where the path difference from the two slits is:
2. Two light sources are described as coherent. This means they have:
3. Why can two separate ordinary light bulbs not produce a stable interference pattern on a screen?
4. A student running a double slit experiment with red light switches to blue light without changing any other part of the apparatus. The fringes will:
5. For monochromatic light passing through a single slit of width a, the dark bands (minima) in the pattern occur at angles satisfying:
6. The grating element d of a diffraction grating is best described as:
7. Diffraction effects are most pronounced when the width of the aperture is:
8. A diffraction grating is preferred over a prism for precise spectroscopy mainly because:
9. Polarisation of light is only possible because light is a...
10. When unpolarised light passes through a single ideal polarising filter, the transmitted intensity is...
11. Malus's Law gives the intensity of polarised light after passing through an analyser as...
12. Young's double-slit experiment demonstrates light interference because...
13. In a double-slit experiment, the fringe spacing Δy is given by...
14. Huygens' principle states that every point on a wavefront acts as...
15. Diffraction is most pronounced when the wavelength of light is...
SA1. Define coherent sources and state the path-difference conditions for constructive and destructive interference. (4 marks)
SA2. Light of wavelength 500 nm passes through slits 0.25 mm apart onto a screen 2.0 m away. Calculate the fringe spacing and state the approximation used. (4 marks)
SA3. A grating has 600 lines per millimetre. Calculate its slit spacing and the first-order angle for 500 nm light at normal incidence. (4 marks)
SA4. Unpolarised light of intensity 120 W m$^{-2}$ passes through a polariser and an analyser at 60°. Calculate the final intensity and state why the first step is separate from Malus’s law. (4 marks)
SA5. Compare one successful prediction and one limitation of a classical wave model of light. (4 marks)
Coherent sources have the same frequency and a constant phase difference. Constructive interference occurs for $\Delta r=n\lambda$; destructive interference occurs for $\Delta r=(n+\tfrac12)\lambda$, where $n=0,1,2,\ldots$.
$\Delta x=\lambda L/d=(500\times10^{-9})(2.0)/(0.25\times10^{-3})=4.0\times10^{-3}$ m = 4.0 mm. This uses the far-screen/small-angle approximation with coherent, effectively monochromatic illumination.
$d=1/(600\times10^3)=1.67\times10^{-6}$ m. With $d\sin\theta=n\lambda$ and $n=1$, $\sin\theta=0.300$, so $\theta=17.5°$.
The first ideal polariser transmits half: $I_1=60$ W m$^{-2}$. Then $I=I_1\cos^260°=15$ W m$^{-2}$. The half-intensity rule applies to unpolarised incident light; Malus’s law applies to already plane-polarised light.
Wave superposition predicts interference and diffraction, and transverse oscillations account for polarisation. A classical continuous-energy wave model cannot account for the photoelectric threshold and the dependence of maximum electron kinetic energy on frequency; a quantum photon model is required for those interactions.