Question 1a

Marks: 2

When electromagnetic waves are reflected from a shiny surface, such as a road sign, they often become polarised.

(a)

Suggest how to determine experimentally if visible light reflected from a road sign is polarised.

[2]

Key Concepts

Polarisation
Polarised, Reflected & Transmitted Beams

Question 1b

Marks: 2

Changes in phase can occur when electromagnetic waves are reflected from a surface.

If an electromagnetic wave is reflected at the boundary between a medium with a higher refractive index than the medium it is travelling in, the oscillating electric field undergoes a phase change of π radians.

Light is incident on an air-water boundary. A displacement-position sketch of the amplitude of the incident electric field is shown. The origin represents the boundary.

4-3-ib-sl-hard-sqs-q1b-question

(b)

Sketch the amplitude of the reflected electric field on the graph.

[2]

Key Concepts

Amplitude & Intensity

Question 1c

Marks: 3

Three polaroid filters P₁, P₂ and P₃ are aligned as follows:

4-3-ib-sl-hard-sqs-q1c-question

Unpolarised light is incident on P₁ and subsequently passes through each of the three polaroid filters. P₁ and P₂ are in fixed positions, but P₃ can be rotated to any angle θ to P₁.

(c)

Determine the angles of θ at which minima and maxima of emergent light intensity occur.

[3]

Key Concepts

Polarisation
Polarised, Reflected & Transmitted Beams

Question 1d

Marks: 3

(d)

Complete the missing spaces in the table to show whether the waves listed are polarised or unpolarised, and to give a reason for your answer.

Wave	Polarised or unpolarised	Reason
Light from the sun
Compression waves caused by an earthquake	Unpolarised	Longitudinal waves cannot be polarised
Electromagnetic waves emitted from a dipole aerial
Ultrasonic waves from an echo sounder

[3]

Key Concepts

Polarisation

Question 2a

Marks: 3

Two coherent sources, A and B, which are in phase with each other, emit microwaves of wavelength 40.0 mm. The amplitude of waves from source B is twice that of source A.

A detector is placed at the point P where it is 0.93 m from A and 1.19 m from B. The centre axis is normal and a bisector to the straight line joining A and B.

4-3-ib-sl-hard-sqs-q2a-question

(a)

With reference to the phase of the microwaves, deduce the magnitude of the detected signal at P and explain your reasoning.

[3]

Key Concepts

Superposition

Question 2b

Marks: 3

(b)

Determine the ratio of the intensity at P to the intensity at O.

[3]

Key Concepts

Amplitude & Intensity

Question 2c

Marks: 5

(c)

Discuss, with suitable calculations, what happens to the detected signal as the detector is moved from P to O.

[5]

Key Concepts

Superposition

Question 2d

Marks: 2

The source B is altered such that it emits waves that are 180° out of phase with source A.

(d)

Deduce the type of interference that now occurs at point P and explain your reasoning.

[2]

Key Concepts

Superposition

Question 3a

Marks: 3

Transverse, sinusoidal progressive waves of wavelength λ have points P and Q which are $\frac{5 λ}{4}$ apart. The waves travel from P to Q.

(a)

With an appropriate sketch, discuss the motion of Q at the instant when P is displaced upwards but is moving downwards.

[3]

Key Concepts

Wavefronts

Question 3b

Marks: 4

Electromagnetic waves, being transverse, can be polarised. A light source is viewed through two pieces of polarisers, A and B, with their axes initially at $\frac{π}{2}$ radians from each other:

4-3-ib-sl-hard-sqs-q3b-question

(b)

Using the axes below, sketch the variation of intensity of light reaching the eye with angular displacement of B with respect to A when polariser B is rotated.

4-3-ib-sl-hard-sqs-q3b-question-diagram-2

[4]

Key Concepts

Superposition
Amplitude & Intensity

Question 3c

Marks: 3

A common incorrect way of drawing this graph is as:

4-3-ib-sl-hard-sqs-q3c-question

(c)

State the differences between the correct graph in part b, and then, through derivation of Malus' Law, explain why the graph above is incorrect.

[3]

Key Concepts

Amplitude & Intensity
Superposition

Question 4a

Marks: 3

Plane polarised electromagnetic waves are incident on an aerial positioned to give a maximum response. High winds cause the aerial to rotate about the direction of the incident wave until it makes and angle of 40° to the plane of polarisation.

4-3-ib-sl-hard-sqs-q4a-question

(a)

Calculate the percentage reduction in the amplitude of the signal received by the aerial following the high winds.

[3]

Key Concepts

Malus's Law

Question 4b

Marks: 3

The intensity of incident radiation is 0.05 mW m⁻². When the aerial is repaired, it is found to have a maximum vibration amplitude of 6.3 mm.

(b)

Determine the angle at which the aerial has been set.

[3]

Key Concepts

Malus's Law

DP IB Physics: SL

Topic Questions

4.3 Wave Characteristics

Question 1a

Key Concepts

Question 1b

Key Concepts

Question 1c

Key Concepts

Question 1d

Key Concepts

Question 2a

Key Concepts

Question 2b

Key Concepts

Question 2c

Key Concepts

Question 2d

Key Concepts

Question 3a

Key Concepts

Question 3b

Key Concepts

Question 3c

Key Concepts

Question 4a

Key Concepts

Question 4b

Key Concepts

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