Syllabus Edition

First teaching 2014

Last exams 2024

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Wave Behaviour (DP IB Physics: SL)

Exam Questions

3 hours44 questions
1a
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2 marks

State what is meant by: 

(i)
The law of reflection.
[1]
(ii)
Refraction.
[1]
1b
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2 marks

The following diagram shows an incident ray perpendicular to the boundary between two media.

4-4-1b-question-stem-sl-sq-easy-phy

Complete the ray diagram by drawing the transmitted ray.

1c
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2 marks

Ray diagrams can be used to show reflection and refraction. The following diagram shows the reflection of light on a smooth surface.

4-4-1c-question-stem-sl-sq-easy-phy

On the ray diagram label: 

(i)
The incident ray.
[1]
(ii)
The reflected ray.
[1]
1d
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3 marks

The ray diagram shows an incident ray on a plane mirror.

4-4-1d-question-stem-sl-sq-easy-phy

Calculate the angle of reflection.

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2a
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2 marks

Refraction occurs when light travels between media with different optical densities.

Describe what happens when light passes from a less dense medium into a more dense medium in terms of: 

(i)
The relative sizes of the angles of incidence and refraction.
[1]
(ii)
The direction of the refracted light ray in relation to the normal.
[1]
2b
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3 marks

The refractive index is calculated using the equation:

nc over v

Write in the missing information to complete the following table:

 

Quantity

Symbol

Units

 

n

No units

 

c

 

Speed of light in medium

 v

 

2c
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1 mark

Define the term critical angle.

2d
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2 marks

Incident light travelling through water approaches the surface of the water and meets the boundary with air. The incident ray has an angle of incidence = 40°.

4-4-2d-question-stem-sl-sq-easy-phy

The refractive index of air is 1.00 and the refractive index of water is 1.33.

Calculate the angle of refraction for the refracted ray.

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3a
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1 mark

Define diffraction.

3b
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5 marks

The diagram shows a student in a room with an open door and a television in the next room. 

4-4-3b-question-stem-sl-sq-easy-phy

The student can hear the sound of the television, but cannot see the picture coming from it. 

Complete the following sentences by circling the correct word to explain why this is the case. 

 

Sound waves emitted from the television diffract / refract around the opening of the door because the amplitude / wavelength is similar in size to the door. The amplitude / wavelength of light is much larger / smaller than that of the sound waves, so light is not not diffracted / refracted around the opening of the door.

3c
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1 mark

Define coherence.

3d
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4 marks
The diagram shows two different waves from sources s1 and s2 meeting at point P
.
 
4-4-3d-question-stem-sl-sq-easy-phy
 

For the waves meeting at point P: 

(i)
Determine the path difference.
[3]
(ii)
State whether the interference will be constructive or destructive.
[1]

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4a
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1 mark

Outline the conditions for destructive interference.

4b
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1 mark

Some light can be described as monochromatic.

State what is meant by the term monochromatic.

4c
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4 marks

The diagram shows the wave fronts emitted from two point sources s1 and s2

4-4-4c-question-stem-sl-sq-easy-phy

The waves meet at point P.

 
(i)
By considering the number of waves, determine the path difference.
[3]
(ii)
State whether constructive or destructive interference would occur at point P.
[1]
4d
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2 marks

The diagram shows two sources of coherent light producing a double-slit interference pattern. 

4-4-4d-question-stem-sl-sq-easy-phy

State whether the interference is constructive or destructive at point:

 
(i)
A.
[1]
(ii)
B.
[1]

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5a
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3 marks

The distance between the bright fringes in a double-slit interference pattern can be determined by the double-slit equation

sfraction numerator lambda D over denominator d end fraction

Draw a line to match the quantity to the correct symbol.

double-slit-eq
5b
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2 marks

Red laser light is used to form a double-slit interference pattern on a screen.

4-4-5b-question-stem-sl-sq-easy-phy

The distance between the bright fringes depends on the wavelength of the incident light.

Outline how the interference pattern would be affected if blue laser light were used instead.

5c
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4 marks

Red laser light of wavelength λ = 650 nm is used to form a double-slit interference pattern on the screen as shown. 

4-4-5b-question-stem-sl-sq-easy-phy

The separation distance of the slits d = 0.2 mm, and the distance between the slits and the screen D = 1.2 m.

Calculate the separation distance between the fringes on the screen s.

5d
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2 marks

For the interference pattern shown in part (c):

4-4-5d-question-stem-sl-sq-easy-phy

Explain why there is no bright fringe at point X.

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1a
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2 marks

A beam of monochromatic light is incident upon two slits. The distance between the slits is 0.4 mm.

q1a_wave-behaviour_ib-sl-physics-sq-medium

A series of bright and dark fringes appear on the screen. Explain how a bright fringe is formed.

1b
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2 marks

Monochromatic light is incident on the double-slits and the distance from the screen is 0.64 m. The distance between the bright fringes is 9.3 × 10–4 m. Determine the wavelength of the incident light.

1c
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2 marks

If the wavelength of the incident light is halved and the distance between the slits is doubled, outline the effect on the separation of the fringes of the interference pattern.

1d
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2 marks

One of the slits is covered so it emits no light.

Describe how this changes the pattern's appearance and the intensities observed on the screen.

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2a
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3 marks

Light is incident upon a piece of glass.

q2a_wave-behaviour_ib-sl-physics-sq-medium

The angle of incidence is less than that of the critical angle. The refractive index of the glass is 1.50.

Explain what is meant by the 'critical angle' and what will occur at angles that are above and below the critical angle.

2b
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2 marks

The angle of incidence for this situation is 34°.

Determine the angle of refraction to the nearest degree.

2c
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2 marks

The refracted light travels within the glass for 5 m.

Determine the time that the light will take to travel this distance in the glass.

2d
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3 marks

The light continues within the glass until it strikes the side perpendicular to the original side of entry.

q2d_wave-behaviour_ib-sl-physics-sq-medium

Show that the light will not emerge from the side of the glass.

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3a
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2 marks

The diagram shows a cross-section through a step-index optical fibre.

QsFjbj7I_q3a_wave-behaviour_ib-sl-physics-sq-medium

Beam A is incident at the end of the optical fibre at an angle of 12.6° to the normal and refracts into the core at 6.89° to the normal.

Calculate the refractive index of the core.

3b
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2 marks

Beam A travels through the air-core boundary and experiences total internal reflection.

On the diagram, show the path of this ray down the fibre and label the angle of reflection.

3c
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2 marks

Beam B is incident at the same end of the fibre. It refracts through the air-core boundary and then refracts again when it hits the core-cladding boundary at an angle of 51.8°, traveling along the boundary.

Calculate the refractive index of the cladding.

3d
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3 marks

A different step-index optical fibre is built with the same core as that in part (a) but with a different material used for the cladding.

The speed of light in the new cladding material is 1.54 × 108 m s1.

Explain why this new cladding material would not be suitable for sending signals through the step-index optical fibre. Use a calculation to support your answer.

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4a
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2 marks

A laboratory ultrasound transmitter emits ultrasonic waves of wavelength 0.7 cm through two slits. A receiver, moving along line AB, parallel to the line of the slits, detects regular rises and falls in the strength of the signal.

A student measures a distance of 0.39 m between the first and the fourth maxima in the signal when the receiver is 1.5 m from the slits.

_fKjM6aZ_q4a_wave-behaviour_ib-sl-physics-sq-medium

The ultrasound transmitter is a coherent source.

Explain what is meant by the term coherent source.

4b
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4 marks

Explain why the receiver detects regular rises and falls in the strength of the signals as it moves along the line AB.

4c
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3 marks

Calculate the distance between the two slits.

4d
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3 marks

One of the slits is now covered. No other changes are made to the experiment.

State and explain the difference between the observations made as the receiver is moved along AB before and after one of the slits is covered.

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5a
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2 marks

White light is passed through a single narrow slit and illuminates a screen.

Describe the patten observed on the screen.

5b
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2 marks

Blue light from a laser is now passed through a single narrow slit. A pattern of bright and dark regions can be observed on the screen which is placed several meters beyond the slit.

GNKZBEq6_q5b_wave-behaviour_ib-sl-physics-sq-medium

Describe the effect on the diffraction pattern if the width of the narrow slit is decreased. 

5c
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3 marks

With the original slit width, state and explain the effect on the width of the fringes on the diffraction pattern if the blue light is replaced with a red light of the same intensity.

5d
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3 marks

The intensity graph for the diffracted blue light is shown in the diagram below.

GcPIFIAd_q5d_wave-behaviour_ib-sl-physics-sq-medium

On the axes of the diagram, sketch the intensity graph for the laser emitting red light.

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1a
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3 marks

A student designs an experiment to replicate Young’s double slit demonstration. The student uses a candle as a light source, with a piece of coloured filter paper to produce monochromatic light. They then consider additional apparatus required in order to observe an interference pattern. 

Sketch a diagram, labelling all apparatus, as well as any important quantities, to show the setup the student should use to produce and observe an interference pattern. 

1b
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4 marks

The student labels the two slits on the double-slit grating slit X and slit Y. The student then paints over slit X, such that the intensity of light emerging from it is 50% of that emerging from slit Y. 

Discuss the effects this change will have on the student’s observations. 

1c
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4 marks

The student finishes setting up their apparatus and makes a quick note of two separate measurements, 0.75 mm and 2.0 m.

They then plot a graph of the intensity of light against the distance from the centre of the screen, represented by the origin.

4-4-ib-sl-hard-sqs-q1c-question

Determine which colour of filter paper the student most likely chose for this experiment.  

1d
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2 marks

Determine the phase angle between the waves meeting at the point that is 2.8 mm from the centre of the screen.

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2a
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2 marks

A ray of light passes from air into a glass prism.

4-4-ib-sl-hard-sqs-q2a-question

As the light ray passes through the prism, it emerges back into the air.

Calculate the critical angle from the glass to the air.

2b
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2 marks

On the diagram from part (a), draw the continuation of the path of the ray of light until it emerges back into the air, labelling the values of the angles between the ray and any normals.

2c
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3 marks

The prism is rotated and one side is coated with a film of transparent gel. A ray of light strikes the prism, at an angle of incidence of 38°, and continues through the glass to strike the glass–gel boundary at the critical angle.

4-4-ib-sl-hard-sqs-q2c-question

Calculate the refractive index of the gel.

2d
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2 marks

A ray of light now strikes the prism at an angle of incidence which means that it now refracts straight through the gel at the glass–gel boundary.

Without calculation, explain how the critical angle for the glass–gel boundary differs from the critical angle for the gel–air boundary.

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3a
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3 marks

A soap bubble is known as a ‘thin film’. There is a thin layer of water trapped between soap molecules on either side.

4-4-ib-sl-hard-sqs-q3a-question-diagram-1

Light that hits the bubble behaves in very predictable ways, resulting in visually interesting and colourful effects.

Blue light of wavelength 400 nm is incident at an angle theta on a bubble where it splits into a ray that is reflected (ray alpha) and a ray which refracts into the bubble (ray beta). Ray beta reflects from the other side of the film, and then leaves the bubble again. 

4-4-ib-sl-hard-sqs-q3a-question-diagram-2

Upon reflection, ray alpha undergoes a phase shift of pi radians. Ray beta does not undergo any phase shift upon reflection. 

Determine an expression for the path difference between ray alpha and ray beta, justifying your answer.

3b
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3 marks

Thin-film interference occurs when reflected light from two different boundaries interfere. 

With reference to the path difference, describe the conditions for constructive and destructive thin-film interference of ray alpha and beta from part a.

3c
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4 marks

For a given angle of incidence θ, discuss what will be observed above the surface of the bubble for different colours of light. 

3d
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4 marks

Anti-reflective coatings use thin-film interference effects to make it appear that light is not reflected from the surface and instead passes straight through it. A simplified version of anti-reflective coated glass is shown in the diagram:

4-4-ib-sl-hard-sqs-q3d-question

The coating is designed such that there is a phase shift of pi radians at the first boundary (between the air and the coating) as well as at the second boundary (between the coating and the glass). 

By considering the conditions for constructive or destructive interference, discuss the limitations of this design. 

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4a
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2 marks

The tube of an endoscope behaves like an optical fibre to examine the interior of the body for medical diagnosis. One end of the fibre is illuminated and an image of the inside of the stomach is viewed by the doctor.

4-4-ib-sl-hard-sqs-q4a-question

Draw on the picture the complete path of the light from the illumination to the doctor.

4b
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4 marks

The diagram shows a cross–section through an optical fibre used in an endoscope. The critical angle is 7% lower than the 75º angle to the normal at the core–cladding boundary. The refractive index of the cladding is 1.4.

4-4-ib-sl-hard-sqs-q4b-question

Calculate the angle of incidence theta subscript i at the air–core boundary.

4c
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3 marks

Complete the graph to show how the refractive index changes with radial distance along the line ABCD in Figure 2.

4-4-ib-sl-hard-sqs-q4c-question

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