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Topic C.3 · HL only

Wave Phenomena: notes and practice questions

4 min read Jump to 7 practice questions
Summary
  • This topic extends the understanding of wave phenomena to include higher level concepts of diffraction and interference.
  • Single-slit diffraction intensity patterns are described by θ=λb\theta = \frac{\lambda}{b}, where θ\theta is the angle to the first minimum, λ\lambda is the wavelength, and bb is the slit width.
  • The single-slit pattern modulates the double-slit interference pattern.
  • Interference patterns from multiple slits and diffraction gratings are given by nλ=dsin⁡θn\lambda = d \sin \theta, where nn is the order of the maximum, λ\lambda is the wavelength, dd is the slit separation, and θ\theta is the angle to the maximum.

How it is examined

All three papers, and one of the most productive Paper 1B topics because refraction and double-slit experiments both linearize cleanly. May 2025 Paper 1B TZ1 question 2 was a semi-circular glass block investigation across seven marks, including drawing a maximum-gradient line and quoting a refractive index with its uncertainty. May 2025 Paper 1B TZ3 question 2 was a double-slit determination of λ\lambda. In Paper 2 the standard 3-mark shape is: find the angle of incidence, compare with the critical angle, conclude. Single-slit and grating questions are HL only.

Given in the booklet

SL: Snell's law in the three-part form above, both path-difference conditions, s=λD/ds = \lambda D/d. HL adds θ=λ/b\theta = \lambda/b and nλ=dsin⁡θn\lambda = d\sin\theta. Note the direction of the Snell ratio in the booklet: n1/n2=sin⁡θ2/sin⁡θ1n_1/n_2 = \sin\theta_2/\sin\theta_1, which is the reciprocal of the arrangement many textbooks print. A student who copies it straight out gets it right; a student working from memory often inverts it. Refractive indices of named materials are given in the question, not the booklet.

Key ideas
  • that waves travelling in two and three dimensions can be described through wavefronts and rays
  • wave behaviour at boundaries in terms of reflection, refraction and transmission
  • wave diffraction around a body and through an aperture
  • wavefront-ray diagrams showing refraction and diffraction

Guiding questions

  • How are observations of wave behaviours at a boundary between different media explained?
  • How is the behaviour of waves passing through apertures represented?
  • What happens when two waves meet at a point in space?

Linking questions

  • What can an understanding of the results of Young's double-slit experiment reveal about the nature of light?
  • What evidence is there that particles possess wave-like properties such as wavelength? (NOS)

Practice questions

7 questions · 6 medium · 1 hard
Showing 7 of 7

Question 1

MediumPaper 2 · calculator4 marks

A scientist is conducting an experiment using a diffraction grating to analyze the spectrum of a green laser. The laser emits light with a wavelength of 532532 nm, incident normally on the grating. The scientist wants to ensure that the third-order maximum is just visible on a screen placed far away.

(a) Determine the maximum number of lines per millimeter that the diffraction grating can have for the third-order maximum to be just visible.

Question 2

HardPaper 2 · calculator8 marks
(a)

A research team is developing a high-resolution spectrometer for analyzing light from distant astronomical sources. The core component is a diffraction grating with 300 lines per mm. When light of a specific spectral line, with a wavelength of 630 nm, is incident normally on the grating.

(a) Calculate the angular position of the first-order maximum.

[2]
(b)(i)

(b) The entrance slit of the spectrometer, which acts as the source for the grating, has a finite width of 2.0×10−52.0 \times 10^{-5} m.

(i) Sketch a graph to show the variation, with angle, of the relative intensity of the diffraction pattern produced by this single slit.

[3]
(b)(ii)

(ii) Suggest whether the fifth-order spectral line (maximum) from the diffraction grating would be clearly observable for this spectrometer setup. Justify your answer.

[3]

Question 3

MediumPaper 2 · calculator3 marks

A student conducts an experiment to investigate the diffraction of monochromatic light. A laser beam passes through a single narrow slit and projects a diffraction pattern onto a screen located a distance of 2.82.8 m from the slit.

The slit has a width of 0.0750.075 mm. The measured width of the central maximum on the screen is 5.25.2 cm.

(a) Calculate the wavelength of the laser light.

Question 4

MediumPaper 1A · calculator1 mark

Monochromatic light of wavelength 5.0×10−75.0 \times 10^{-7} m is incident normally on a diffraction grating. The grating has a line spacing of 2.5×10−62.5 \times 10^{-6} m. How many diffraction maxima are present in the transmitted light?

A. 55

B. 99

C. 1111

D. 1313

Question 5

MediumPaper 1A · calculator1 mark

Two coherent laser beams, originating from the same source, travel different paths to converge at point P on a screen. The path length for one beam is 5.20×10−65.20 \times 10^{-6} m, and for the other beam, it is 6.70×10−66.70 \times 10^{-6} m.

At point P, a dark fringe (minimum intensity) is observed.

What is a possible wavelength of the laser light?

A. 429 nm429 \text{ nm}

B. 500 nm500 \text{ nm}

C. 600 nm600 \text{ nm}

D. 750 nm750 \text{ nm}

Question 6

MediumPaper 1A · calculator1 mark

Monochromatic light is incident normally on a diffraction grating. A pattern of maxima is observed on a screen. The grating is replaced by one with a greater number of lines per millimetre.

What is the effect on the angular separation of the maxima and the maximum observed order?

A. Angular separation increases and maximum observed order increases

B. Angular separation increases and maximum observed order decreases

C. Angular separation decreases and maximum observed order increases

D. Angular separation decreases and maximum observed order decreases

Question 7

MediumPaper 1A · calculator1 mark

Monochromatic light of wavelength 600 nm600 \text{ nm} is incident on a single slit, producing a diffraction pattern. The first diffraction minimum is observed at an angle of 3.0×10−3 rad3.0 \times 10^{-3} \text{ rad} from the central maximum.

If the light source is replaced with another monochromatic source of wavelength 450 nm450 \text{ nm}, what will be the new angle of the first diffraction minimum, assuming the slit width remains unchanged?

A. 4.0×10−3 rad4.0 \times 10^{-3} \text{ rad}

B. 2.25×10−3 rad2.25 \times 10^{-3} \text{ rad}

C. 3.0×10−3 rad3.0 \times 10^{-3} \text{ rad}

D. 1.8×10−3 rad1.8 \times 10^{-3} \text{ rad}

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Where marks are lost

  • Stopping one step short of the conclusion. Two numbers and no sentence is two marks out of three.
  • Answering a procedure question with a platitude.
  • Losing precision in Paper 1B. Uniquely to this paper, quoting the right number badly loses marks.
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What does Wave Phenomena cover in IB Physics?

This topic extends the understanding of wave phenomena to include higher level concepts of diffraction and interference. Single-slit diffraction intensity patterns are described by θ = (λ)/(b), where θ is the angle to the first minimum, λ is the wavelength, and b is the slit width. The single-slit pattern modulates the double-slit interference pattern.

Is Wave Phenomena SL or HL?

Wave Phenomena is HL only. SL students are not examined on it.

How do I revise Wave Phenomena for IB Physics?

Start from the core idea: this topic extends the understanding of wave phenomena to include higher level concepts of diffraction and interference. In the exam: all three papers, and one of the most productive Paper 1B topics because refraction and double-slit experiments both linearize cleanly. May 2025 Paper 1B TZ1 question 2 was a semi-circular glass block investigation across seven marks, including drawing a maximum-gradient line and quoting a refractive index with its uncertainty. Then practise exam-style questions, easiest first, writing out every step of your working before you check it.

How does FourtyFive help me practise Wave Phenomena?

FourtyFive has 7 Wave Phenomena questions. Every answer you write is marked mark by mark, IB-style, and you see where each mark was won or lost. Every part has a hint, the AI tutor helps you through the step you are stuck on, and your Study Profile picks what to practise next.

Is FourtyFive free for Wave Phenomena practice?

Yes. A free account gives you 50 marked answers a month, and you do not need a card to sign up.

Can I handwrite Wave Phenomena answers on an iPad?

Yes. In the FourtyFive iPad app you write your working by hand with Apple Pencil, the way you would on paper, and it is marked the same way.

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