What does Wave Phenomena cover in IB Physics?

This topic describes wave behaviour, including reflection, refraction, diffraction, and interference. Waves are represented by wavefronts and rays, reflecting, refracting, and transmitting at boundaries. Diffraction occurs around bodies and apertures, visualized with wavefront-ray diagrams.

Is Wave Phenomena SL or HL?

Both. SL and HL students study Wave Phenomena, and HL goes further: single-slit diffraction including intensity patterns, as given by θ = dfracλb, where b is the slit width.

How does FourtyFive help me practise Wave Phenomena?

FourtyFive has 15 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.

Topic C.3 · SL and HL

Wave Phenomena: notes and practice questions

Q: How do I revise Wave Phenomena for IB Physics?

Start from the core idea: this topic describes wave behaviour, including reflection, refraction, 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.

9 min read Jump to 15 practice questions

Summary

This topic describes wave behaviour, including reflection, refraction, diffraction, and interference.
Waves are represented by wavefronts and rays, reflecting, refracting, and transmitting at boundaries.
Diffraction occurs around bodies and apertures, visualized with wavefront-ray diagrams.
Snell's law: $\frac{n_1}{n_2} = \frac{\sin \theta_2}{\sin \theta_1} = \frac{v_2}{v_1}$ , critical angle, and total internal reflection.
Superposition leads to interference; double-source interference requires coherent sources.
Constructive interference: path difference $= n\lambda$ . Destructive interference: path difference $= (n + \frac{1}{2})\lambda$ .
Young's double-slit fringe separation: $s = \frac{\lambda D}{d}$ .

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 $\lambda$ . 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, $s = \lambda D/d$ . HL adds $\theta = \lambda/b$ and $n\lambda = d\sin\theta$ . Note the direction of the Snell ratio in the booklet: $n_1/n_2 = \sin\theta_2/\sin\theta_1$ , 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

At HL

single-slit diffraction including intensity patterns, as given by $\theta = \dfrac{\lambda}{b}$ , where b is the slit width
that the single-slit pattern modulates the double-slit interference pattern
interference patterns from multiple slits and diffraction gratings, as given by $n\lambda = d\sin\theta$

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

15 questions · 3 easy · 11 medium · 1 hard

Showing 15 of 15

Question 1

EasyPaper 1A · calculator1 mark

A ray of monochromatic light travels from air and enters a block of glass. Part of the light is refracted.

Three statements are made about the refracted light compared to the incident light.

I. The speed of the light is different.

II. The frequency of the light is different.

III. The wavelength of the light is different.

Which of the statements are correct?

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

Question 2

MediumPaper 1A · calculator1 mark

Microwaves of wavelength $\lambda$ are emitted from two identical horn antennas. The antennas act as single slits of width $b$ and their centres are separated by a distance $d$ . A detector measures the intensity of the microwaves at different angles $\theta$ from the central axis.

The resulting intensity pattern is shown.

$Graph of microwave intensity versus angle theta. A central diffraction peak contains several smaller interference fringes. The first interference maximum to the side of the central one is at an angle of 0.02 rad. The first minimum of the overall diffraction pattern is at an angle of 0.08 rad.$

What are the approximate values of the ratios $\frac{\lambda}{d}$ and $\frac{\lambda}{b}$ ?

	$\frac{\lambda}{d}$	$\frac{\lambda}{b}$
A.	$0.08$	$0.02$
B.	$0.02$	$0.08$
C.	$0.04$	$0.16$
D.	$0.02$	$0.04$

Question 3

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 $2.0 \times 10^{-5}$ 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 4

EasyPaper 1A · calculator1 mark

A pulse of monochromatic light travelling in air is incident on a diamond block. Part of the pulse is transmitted into the diamond.

Three statements are made about the transmitted pulse compared to the incident pulse.

I. The wavelength is different.

II. The amplitude is different.

III. The frequency is different.

Which of the statements are correct?

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

Question 5

MediumPaper 1A · calculator1 mark

An optical fibre consists of a core with refractive index $n_{core}$ and a cladding with refractive index $n_{clad}$ . Light travels from the core to the cladding.

The refractive index of the core is $1.60$ and the refractive index of the cladding is $1.45$ .

What is the critical angle for total internal reflection at the core-cladding interface?

A. $25.0^{\circ}$

B. $43.6^{\circ}$

C. $65.0^{\circ}$

D. $72.5^{\circ}$

Question 6

EasyPaper 1A · calculator1 mark

A student directs a beam of monochromatic red light from a laser normally onto a diffraction grating. A pattern of maxima is observed on a screen far from the grating.

The student then replaces the red light source with a source of monochromatic blue light. All other experimental conditions, including the grating and distances, remain the same.

What is the primary change observed in the diffraction pattern on the screen?

A. The angular separation between the maxima increases.

B. The angular separation between the maxima decreases.

C. The number of observable maxima necessarily decreases.

D. The intensity of all maxima increases.

Question 7

MediumPaper 2 · calculator4 marks

(a)

A laser emits green light with a frequency of $5.50 \times 10^{14}$ Hz.

(a) Calculate the wavelength of this light in air.

[2]

(b)

(b) Determine the wavelength of this light when it travels through water, which has a refractive index of $1.33$ .

[2]

Question 8

MediumPaper 1A · calculator1 mark

A laser beam is directed from air into a thick slab of optical glass, which then rests on a layer of liquid ethanol. The interfaces are parallel.

The refractive index of air is $n_{air} = 1.00$ .

The refractive index of optical glass is $n_{glass} = 1.55$ .

The refractive index of liquid ethanol is $n_{ethanol} = 1.36$ .

The angle of incidence of the laser beam at the air-glass interface is $48^{\circ}$ .

What is the angle of refraction in the ethanol layer?

A. $29^{\circ}$

B. $33^{\circ}$

C. $38^{\circ}$

D. $59^{\circ}$

Question 9

MediumPaper 1A · calculator1 mark

Two coherent laser beams, originating from slits $S_1$ and $S_2$ , illuminate a point P on a screen. The wavelength of the light is $6.00 \times 10^{-7}$ m. Point P is located $0.2000000$ m from $S_1$ and $0.2000003$ m from $S_2$ . At point P, the amplitude of the wave from $S_1$ is $x_0$ , and the amplitude from $S_2$ is $4x_0$ .

What is the resultant amplitude at P?

A. $x_0$

B. $2x_0$

C. $3x_0$

D. $5x_0$

Question 10

MediumPaper 1A · calculator1 mark

Two coherent light sources, $S_1$ and $S_2$ , emit light waves of wavelength $600 \text{ nm}$ in phase. A point P is located such that its distance from $S_1$ is $1.0000000 \text{ m}$ and from $S_2$ is $1.0000003 \text{ m}$ . The amplitude of the wave from $S_1$ at P is $A$ , and from $S_2$ at P is $2A$ .

What is the resultant amplitude at P?

A. $3A$

B. $A$

C. $\sqrt{5}A$

D. $2A$

Question 11

MediumPaper 1A · calculator1 mark

Two coherent point sources of light, operating in phase, emit monochromatic light. A detector at point P registers a minimum intensity (dark fringe).

Point P is located at a distance of $2.000000 \text{ m}$ from one source and $2.0000015 \text{ m}$ from the other.

What is a possible wavelength of the light?

A. $300 \text{ nm}$

B. $450 \text{ nm}$

C. $600 \text{ nm}$

D. $900 \text{ nm}$

Question 12

MediumPaper 1A · calculator1 mark

A new type of optical fibre is being developed using a novel polymer. Light traveling from this polymer core into the surrounding air experiences total internal reflection if the angle of incidence exceeds a certain critical angle.

The critical angle for light passing from the polymer into air is $38.7^\circ$ . The speed of light in vacuum is $3.00 \times 10^8 \text{ m s}^{-1}$ .

What is the approximate value for the speed of light in the polymer?

A. $1.5 \times 10^8\text{ m s}^{-1}$

B. $1.7 \times 10^8\text{ m s}^{-1}$

C. $1.9 \times 10^8\text{ m s}^{-1}$

D. $2.1 \times 10^8\text{ m s}^{-1}$

Question 13

MediumPaper 1A · calculator1 mark

A monochromatic light source illuminates a diffraction grating in air, producing a pattern of principal maxima on a distant screen. A total of 11 principal maxima are observed.

The diffraction grating and the screen are then submerged in water (refractive index $n=1.33$ ). The light source remains in the air, and the beam enters the water before reaching the grating.

What are the changes, if any, to the angular separation of the principal maxima and the total number of principal maxima observed?

Option	Angular separation of maxima	Total number of maxima
A	Decreases	Increases
B	Decreases	Decreases
C	Increases	Increases
D	Increases	Decreases

A. A

B. B

C. C

D. D

Question 14

MediumPaper 1A · calculator1 mark

A student performs a single-slit diffraction experiment using a red laser. The resulting diffraction pattern is observed on a screen. The graph shows the variation of light intensity with position on the screen.

$graph showing intensity versus distance for a single slit diffraction pattern with a central maximum and smaller side maxima$

The student replaces the red laser with a blue laser of the same power output. The slit width and distance to the screen are unchanged.

Which graph correctly shows the new diffraction pattern? The original pattern from the red laser is shown as a dashed line.

graph showing a wider, less intense central maximum with the original curve dashed

graph showing a narrower, more intense central maximum with the original curve dashed

graph showing a wider, more intense central maximum with the original curve dashed

graph showing a narrower, less intense central maximum with the original curve dashed

Question 15

MediumPaper 1A · calculator1 mark

A monochromatic light ray travels from a vacuum into a transparent medium P, and then separately from a vacuum into a transparent medium Q.

The refractive index of medium P relative to vacuum, $n_P$ , and the refractive index of medium Q relative to vacuum, $n_Q$ , are such that:

$\frac{n_P}{n_{\text{vacuum}}} = 1.6$

$\frac{n_Q}{n_{\text{vacuum}}} = 1.2$

What is the ratio $\frac{\text{speed of light in medium P}}{\text{speed of light in medium Q}}$ ?

A. $\frac{4}{3}$

B. $\frac{3}{4}$

C. $1.2$

D. $1.6$

Every Wave Phenomena question, marked for you

Every answer is marked mark by mark, IB-style, and the AI tutor helps when you are stuck.

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.

Wave Phenomena: notes and practice questions

How it is examined

Guiding questions

Linking questions