Free C.3 Wave phenomena questions for IB Physics (SL & HL), part of C Wave behaviour. Each question has the answer and the marking points an examiner would look for.
Generate a full C.3 Wave Phenomena worksheet →All C Wave behaviour questionsIn a double-slit experiment with white light, which statements are correct?
I. Each side fringe is coloured, with red furthest from the centre.
II. Fringes form only if the slits are wider than the wavelength.
III. The central fringe is white.
Answer: B
Monochromatic light of wavelength 600 nm is incident normally on a diffraction grating with 600 lines per mm.
What is the highest order of maximum that can be observed?
Answer: B
Coherent light of wavelength 633 nm is incident on two narrow slits 0.2 mm apart. Fringes are observed on a screen 2 m away.
Explain what is meant by coherent light and why it is needed.
Calculate the fringe spacing.
Explain, in terms of path difference, the formation of a dark fringe.
The apparatus is immersed in water of refractive index 1.33. Calculate the new fringe spacing.
One slit is covered with a filter that halves the intensity of the light passing through it. Describe the effect on the pattern.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | constant phase difference constant phase difference (and same frequency) ✓ so that the interference pattern is stable ✓ | 2 |
| (b) | 6.33 mm s = λDd ✓ 6.33 mm ✓ | 2 |
| (c) | half-wavelength path difference the path difference is an odd number of half wavelengths ✓ waves arrive in antiphase and interfere destructively ✓ | 2 |
| (d) | 4.76 mm wavelength in water = 6331.33 = 476 nm ✓ spacing = 4.76 mm ✓ | 2 |
| (e) | dark fringes less dark fringe positions unchanged ✓ minima are no longer completely dark (and maxima less bright), so contrast is reduced ✓ | 2 |
Light of wavelength 600 nm is incident on a diffraction grating with 400 lines per mm.
Calculate the grating spacing.
Calculate the angle of the second-order maximum.
Determine the total number of maxima observed.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 2.5 × 10−6 m 2.5 × 10−6 m ✓ | 1 |
| (b) | 28.7° sin θ = 2λ/d ✓ 28.7° ✓ | 2 |
| (c) | 9 nmax = 4 ✓ 2 × 4 + 1 = 9 ✓ | 2 |
Two loudspeakers emit sound of frequency 850 Hz in phase. A detector is 4.00 m from one speaker and 4.600 m from the other. The speed of sound in air is 340 m s−1.
Calculate the wavelength of the sound.
Predict whether the detector is at a point of constructive or destructive interference.
The sound reaches the surface of a lake at an angle of incidence of 50°. The speed of sound in water is 1500 m s−1. Predict whether the sound can enter the water.
State one condition required for a stable interference pattern.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 0.400 m λ = 0.400 m ✓ | 1 |
| (b) | destructive path difference = 0.600 m = 1.5λ ✓ half-integer number of wavelengths so destructive ✓ | 2 |
| (c) | no — total internal reflection critical angle = sin−1(340/1500) = 13.1° ✓ 50° > 13.1° ✓ so the sound is totally internally reflected and cannot enter the water ✓ | 3 |
| (d) | coherent sources coherent sources: constant phase difference and same frequency ✓ | 1 |
Light travels from glass of refractive index 1.50 into air.
Calculate the critical angle.
Calculate the angle of refraction for an angle of incidence of 30° in the glass.
Calculate the speed of light in the glass.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 42° sin c = 1/1.50 ✓ c = 41.8° ✓ | 2 |
| (b) | 49° sin r = 1.50 × sin30° ✓ r = 48.6° ✓ | 2 |
| (c) | 2.0 × 108 m s−1 3.00 × 108/1.50 = 2.0 × 108 m s−1 ✓ | 1 |
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Meet Riyaz →Original IB-style practice questions written for mentorriyaz.in. These are not IB past paper questions, and this site is not affiliated with or endorsed by the International Baccalaureate Organization. Updated 2026-11-04. Paper generator · mentorriyaz.in