C.3 Wave phenomena
Practice exam-style IB Physics questions for Wave phenomena, aligned with the syllabus and grouped by topic.
Question 1
A set of straight, parallel wavefronts is drawn for water waves travelling across a ripple tank. What is the direction of the rays?
A.
Opposite to the direction of wave propagation
B.
At 45° to the wavefronts
C.
Perpendicular to the wavefronts
D.
Parallel to the wavefronts
Question 2
A wave crosses a boundary into a medium in which its speed is lower. The frequency of the wave is unchanged. What happens to the wavelength?
A.
It increases
B.
It decreases
C.
It remains unchanged
D.
It becomes zero
Question 3
Plane water waves pass through a gap in a barrier. The greatest diffraction occurs when the gap width is
A.
similar to the wavelength
B.
much larger than the wavelength
C.
much smaller than the wave amplitude
D.
similar to the wave speed
Question 4
Two identical pulses on a rope meet, one displaced upward and the other displaced downward by the same amount. What is the resultant displacement at complete overlap?
A.
Zero
B.
Twice one pulse amplitude upward
C.
Equal to one pulse amplitude upward
D.
Twice one pulse amplitude downward
Question 5
What is required for two sources to be coherent?
A.
They have the same amplitude and different frequencies
B.
They emit waves with randomly varying phase difference
C.
They emit waves that never overlap
D.
They have a constant phase difference and the same frequency
Question 6
For monochromatic light incident normally on a single rectangular slit, the angular position of the first minimum is increased by
A.
increasing the slit width
B.
decreasing the wavelength
C.
increasing the light intensity only
D.
decreasing the slit width
Question 7
A point source produces circular water wavefronts in a ripple tank.
Define a wavefront.
[1]
State the direction of the rays for these circular wavefronts.
[1]
State what the spacing between adjacent wavefronts represents.
[1]
Question 8
A student observes water waves passing through a narrow gap.
Describe the change in shape of the wavefronts after the gap when the gap width is similar to the wavelength.
[1]
State one quantity of the waves that remains unchanged after diffraction in the same medium.
[1]
Question 9
Light travels in a transparent material at 2.00 × 10^8 m s⁻¹. What is the refractive index of the material?
A.
6.00
B.
1.50
C.
0.67
D.
1.00
Question 10
Light is incident from glass of refractive index 1.50 into air. What is the critical angle?
A.
48°
B.
56°
C.
34°
D.
42°
Question 11
In a Young double-slit experiment, λ = 5.0 × 10⁻⁷ m, D = 2.0 m and d = 0.25 mm. What is the fringe separation?
A.
4.0 mm
B.
8.0 mm
C.
0.25 mm
D.
1.0 mm
Question 12
A single-slit diffraction pattern is formed using red light and then using blue light with the same slit. How does the central maximum change for blue light?
A.
It becomes wider because blue light has a shorter wavelength
B.
It disappears because blue light cannot diffract
C.
It has the same width because the slit is unchanged
D.
It becomes narrower because blue light has a shorter wavelength
Question 13
In a real double-slit experiment, the brightness of the equally spaced interference fringes decreases away from the centre mainly because
A.
the slits cease to be coherent at large angles
B.
the fringe spacing becomes larger at large angles
C.
the wavelength changes after passing through each slit
D.
the single-slit diffraction envelope modulates the pattern
Question 14
White light is incident normally on a diffraction grating. Which statement describes the central maximum?
A.
It is absent because different wavelengths cancel
B.
It is violet because violet light has the smallest wavelength
C.
It is white because all wavelengths have zero path difference
D.
It is red because red light has the largest wavelength
Question 15
The number of illuminated slits in a multiple-slit arrangement is increased while the slit spacing remains unchanged. What happens to the principal maxima?
A.
They remain unchanged in width and intensity
B.
They become sharper and remain at the same angular positions
C.
They disappear because subsidiary maxima dominate
D.
They become broader and move closer to the centre
Question 16
Plane water waves travel from deep water into shallow water at an angle to the boundary.
State what happens to the frequency at the boundary.
[1]
Explain why the wavelength changes.
[1]
Question 17
A light ray travels from air into a plastic block of refractive index 1.40. The angle of incidence is 50°.
Calculate the angle of refraction.
[1]
State whether the ray bends towards or away from the normal.
[1]
Question 18
Two wave pulses travel towards each other along a stretched rope.
State the principle of superposition.
[1]
Explain what happens when two equal pulses, one upward and one downward, completely overlap.
[1]
Question 19
Two coherent loudspeakers emit in phase with wavelength 0.80 m. A microphone is placed where the path difference from the speakers is 2.0 m.
Determine whether the interference is constructive or destructive.
[1]
State one reason why equal path-difference conditions may not produce complete silence at a minimum.
[1]
State why the sources must be coherent for a stable pattern.
[1]
Question 20
Monochromatic light of wavelength 5.40 × 10⁻⁷ m is incident normally on a single slit of width 0.150 mm.
Calculate the angle to the first minimum.
[1]
State the angular width of the central maximum.
[1]
Question 21
A single-slit diffraction pattern is observed on a screen. The slit width is then decreased while the incident monochromatic light is unchanged.
Describe the change in width of the central maximum.
[1]
Describe the change in intensity of the pattern.
[1]
Explain the change in width using the diffraction equation.
[1]
Question 22
A diffraction grating has 400 lines mm⁻¹. Light of wavelength 650 nm is incident normally.
Determine the grating spacing.
[1]
Calculate the angle of the first-order maximum.
[1]
Question 23
White light is incident normally on a diffraction grating.
State the colour of the zero-order maximum.
[1]
Compare the angles of the red and violet first-order maxima.
[1]
Explain the comparison in (b).
[1]
Question 24
A ripple-tank experiment investigates water waves crossing from region A to region B at a straight boundary. The visual shows incident and transmitted wavefronts.
State which region has the larger wavelength.
[1]
Determine which region has the larger wave speed.
[1]
Explain why the frequency is the same in both regions.
[1]
Question 25
A double-slit interference pattern is recorded on a screen. The visual shows the positions of several bright fringes relative to the central maximum.
Determine the mean fringe separation from the visual.
[1]
Calculate the wavelength of the light using the given slit separation and screen distance shown in the visual.
[1]
State one assumption required for use of s=λD/d.
[1]
Question 26
A diffraction grating has 500 lines mm⁻¹. Monochromatic light of wavelength 600 nm is incident normally. What is the largest possible order?
A.
3
B.
4
C.
1
D.
2
Question 27
A laser of wavelength 630 nm passes through a single slit of width 0.20 mm. What is the angular width of the central maximum?
A.
1.3 × 10⁻² rad
B.
6.3 × 10⁻³ rad
C.
1.6 × 10⁻³ rad
D.
3.2 × 10⁻³ rad
Question 28
A grating produces a first-order maximum at 18° for light of wavelength 520 nm. What is the grating spacing?
A.
3.2 × 10⁻⁶ m
B.
1.7 × 10⁻⁶ m
C.
5.2 × 10⁻⁷ m
D.
1.6 × 10⁻⁷ m
Question 29
Light in a glass block has a critical angle of 40° at a glass-air boundary.
Define critical angle.
[1]
Determine the refractive index of the glass.
[1]
Question 30
In a Young double-slit experiment, the distance between the slits and screen is 1.80 m. The slit separation is 0.300 mm. The distance across 10 adjacent fringe spacings is 30.0 mm.
Determine the fringe separation.
[1]
Calculate the wavelength of the light.
[1]
Suggest why measuring across 10 fringe spacings improves the result.
[1]
Question 31
A rectangular slit is illuminated by monochromatic light.
State where the first diffraction minimum occurs in terms of wavelength λ and slit width b.
[1]
Explain, using superposition, why a minimum is produced in this direction.
[1]
Question 32
A real double slit has slit separation d and slit width b.
State which quantity mainly determines the separation of the fine interference fringes.
[1]
State which quantity mainly determines the width of the diffraction envelope.
[1]
Explain what is meant by a missing order in this pattern.
[1]
Question 33
A monochromatic beam illuminates a grating with many equally spaced slits. A second grating has the same slit spacing but more illuminated slits.
State what happens to the angular positions of the principal maxima.
[1]
Explain what happens to the intensity of a principal maximum.
[1]
Question 34
A diffraction grating has spacing 1.25 × 10⁻⁶ m. Light of wavelength 500 nm is incident normally.
Determine the maximum possible order.
[1]
Explain why no higher order is observed.
[1]
State what would happen to the maximum order if the wavelength were increased.
[1]
Question 35
A student measures angles for light passing from air into a transparent block. The graph shows sin i against sin r.
State the physical quantity represented by the gradient.
[1]
Use the graph to determine the refractive index of the block.
[1]
Suggest two reasons why the plotted points do not all lie exactly on a straight line.
[1]
Question 36
A microphone is moved along a straight line in front of two coherent loudspeakers emitting the same frequency. The graph shows sound intensity against microphone position.
Identify one position of constructive interference from the graph.
[1]
Identify one position of destructive interference from the graph.
[1]
Explain why the minima are not zero intensity.
[1]
State one change that would make the interference pattern unstable.
[1]
Question 37
The visual shows photographs from a ripple-tank experiment in which plane waves pass through apertures of different widths.
State which aperture produces the greatest diffraction.
[1]
Describe the evidence for this in the visual.
[1]
Suggest why long-wavelength radio waves can sometimes be received behind a hill when shorter-wavelength signals cannot.
[1]
Question 38
A single-slit diffraction pattern is recorded for monochromatic light. The graph shows relative intensity against angle.
Identify the angular position of the first minimum on one side of the central maximum.
[1]
Determine the slit width using the wavelength shown on the graph.
[1]
Describe how the graph would change if the slit width were decreased.
[1]
Question 39
A simulation shows multiple-slit interference patterns for the same slit spacing and wavelength but different numbers of illuminated slits.
Compare the angular positions of the principal maxima in the two patterns.
[1]
Compare the width of the principal maxima.
[1]
Explain the change in peak intensity when the number of illuminated slits increases from N to 2N.
[1]
Question 40
White light is incident normally on a diffraction grating. The visual shows the central maximum and first-order spectra on both sides.
State why the central maximum is white.
[1]
Identify which colour is observed at the largest angle in a first-order spectrum.
[1]
Explain the order of colours using the grating equation.
[1]
Question 41
The visual shows the intensity pattern from a real double slit.
Identify one missing fringe/order in the pattern.
[1]
Explain why this fringe is missing.
[1]
Predict the effect on the number of visible fine fringes inside the central envelope if the slit separation is increased while the slit width is unchanged.
[1]
Question 42
A diffraction grating is used to measure the wavelength of a laser. The table gives the angle θ of each principal maximum for several orders m.
| Order m | Angle θ / ° |
|---|---|
| 1 | 11.0 |
| 2 | 22.3 |
| 3 | 34.8 |
| 4 | 49.5 |
| 5 | 71.9 |
| 6 | not observed |
Plotting sinθ against m gives a straight line. State the quantity represented by the gradient.
[1]
Use the table to determine the wavelength of the laser.
[1]
Explain why a higher order listed as “not observed” may be physically impossible.
[1]
Question 43
A ray of light is directed inside a glass optical fibre surrounded by air.
Define total internal reflection and state the two conditions required for it to occur.
[1]
Explain how total internal reflection allows light to be guided along the fibre, including the role of the critical angle.
[1]
Question 44
A student uses a laser and double slit to determine the wavelength of light.
Outline how the fringe separation should be measured to reduce uncertainty.
[1]
Evaluate the method, explaining how the wavelength is determined and discussing two significant sources of uncertainty or error.
[1]
Question 45
Wavefront-ray diagrams can represent both refraction and diffraction.
State two features that all correct wavefront-ray diagrams should show.
[1]
Compare and contrast refraction at a boundary with diffraction through an aperture, referring to wavefront spacing, ray direction and wave speed.
[1]
Question 46
Two-source interference is observed using water waves, sound waves or light.
Define coherence and state the path-difference conditions for constructive and destructive interference for sources initially in phase.
[1]
Discuss why a stable interference pattern is observed only under particular conditions, referring to coherence, overlap and amplitude.
[1]
Question 47
A monochromatic laser beam is incident normally on a single rectangular slit.
Describe the main features of the single-slit diffraction intensity pattern.
[1]
Explain how the first minimum is produced and how changing slit width affects the pattern.
[1]
Question 48
A student uses a diffraction grating to identify wavelengths in a light source.
Derive or state the grating equation for normal incidence and define its symbols.
[1]
Evaluate the use of a diffraction grating for analysing white light and monochromatic light, including the maximum possible order and experimental uncertainties.
[1]
Question 49
A double-slit experiment is performed first with very narrow slits and then with real slits of finite width.
State the formula for the spacing of the double-slit interference fringes and the formula for the first minimum of a single-slit diffraction pattern.
[1]
Compare and contrast the predicted intensity patterns, explaining the modulation of the double-slit pattern by the single-slit envelope.
[1]
Question 50
Multiple-slit interference is used in spectroscopy.
Explain why increasing the number of illuminated slits changes the sharpness and intensity of the principal maxima.
[1]
Discuss how a diffraction grating can separate wavelengths, including white light, maximum order and the role of the finite width of the slits.
[1]
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