Outline what is meant by
(i) wavefront
[2]
(ii) ray.
[1]
Draw, on the grid below, scale diagrams showing the wavefronts for
(i) a plane wave with a wavelength of 1 cm
[2]
(ii) a circular wave with a wavelength of 1 cm.
[2]
In your diagrams, show the direction of propagation with arrows.
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2 marksOutline what is meant by the principle of superposition.
1 markTwo pulses travel toward one another as shown in the diagram.
Sketch the resultant displacement as the pulses superpose.
1 markTwo pulses travel in opposing directions as shown in the diagram. When the pulses meet, they superpose.
Draw the resultant peak as the pulses superpose.
4 marksDistinguish between the terms constructive interference and destructive interference.
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1 markMonochromatic light from a single source is incident normally on two thin, parallel slits. The interference pattern observed on the screen is shown.
State the order of the bright fringe at X.
5 marksThe following data are available.
Wavelength = 600 nm
Distance to screen = 1.5 m
Calculate
(i) the average distance, in m, between two consecutive fringes
[1]
(ii) the separation of the slits
[2]
(iii) the angle between the centre of the pattern and X.
[2]
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State what is meant by:
(i) the law of reflection
[1]
(ii) refraction.
[1]
2 marksThe following diagram shows an incident ray perpendicular to the boundary between two media.
Complete the ray diagram by drawing the transmitted ray.
The diagram shows the reflection of a light ray on a smooth surface.
On the ray diagram label:
(i) the incident ray.
[1]
(ii) the reflected ray.
[1]
The ray diagram shows an incident ray on a plane mirror.
Calculate the angle of reflection.
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Outline what is meant by critical angle.
4 marksA light ray is incident on an air-water boundary. The incident ray makes an angle of 40° with the normal.
The refractive index of air is 1.00, and the refractive index of water is 1.33.
Calculate
(i) the angle the refracted ray makes with the normal
(ii) the critical angle.
Explain the change in the wavelength of the light at the air-water boundary.
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Outline what is meant by coherence.
The diagram shows two different waves from sources S1 and S2 meeting at point P.
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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Outline the condition for destructive interference.
Some light can be described as monochromatic.
State what is meant by the term monochromatic.
4 marksThe diagram shows the wave fronts emitted from two point sources S1 and S2.
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]
The diagram shows two sources of coherent light producing a double-slit interference pattern.
State whether the interference is constructive or destructive at point:
(i) A
[1]
(ii) B
[1]
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In a double-slit experiment, red laser light of wavelength 650 nm is incident on two slits, S1 and S2. The interference pattern is observed on a screen as shown.
The separation of the slits is 
= 0.2 mm, and the distance between the slits and the screen is 
= 1.2 m.
Outline how the interference pattern observed on the screen would change if blue laser light were used instead.
2 marksCalculate the distance 
between the fringes on the screen.
No bright fringe is observed on the screen at point X.
Explain why.
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Two microwave transmitters are placed 15 cm apart and connected to the same source. A receiver is placed 70 cm away and moved along a line parallel to the transmitter. The receiver detects alternating maxima and minima of intensity.
Explain the formation of the intensity maxima and minima.
Outline why the two sources must be coherent for the maxima and minima to be detected.
3 marksThe receiver initially detects an intensity maximum at a point equidistant from the sources. Two minima, X1 and X2, are detected on either side of this maximum.
Calculate, in radians, the angular separation of X1 and X2.
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2 marksA beam of monochromatic light is incident upon two slits. The distance between the slits is 0.4 mm.
A series of bright and dark fringes appear on the screen. Explain how a bright fringe is formed.
2 marksMonochromatic 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.
Calculate the wavelength of the incident light.
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.
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3 marksLight is incident upon a piece of glass.
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.
2 marksThe angle of incidence for this situation is 34°.
Determine the angle of refraction to the nearest degree.
2 marksThe refracted light travels within the glass for 5 m.
Determine the time that the light will take to travel this distance in the glass.
3 marksThe light continues within the glass until it strikes the side perpendicular to the original side of entry.
Show that the light will not emerge from the side of the glass.
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2 marksThe diagram shows a cross-section through a step-index optical fibre.
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.
2 marksBeam 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.
2 marksBeam 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.
3 marksA 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 s−1.
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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A beam of microwaves is incident normally on a pair of identical narrow slits S1 and S2.
When a microwave receiver is initially placed at W, which is equidistant from the slits, an intensity maximum is observed. The receiver is then moved towards Z along a line parallel to the slits. Intensity maxima are also observed at X and Y, with one minimum between them. W, X and Y are consecutive maxima.
Explain the formation of
(i) the intensity maxima at W, X, and Y
[2]
(ii) the intensity minima between W, X, and Y.
[2]
2 marksThe distance from S1 to Y is 1.482 m, and the distance from S2 to Y is 1.310 m.
Calculate the wavelength of the microwaves.
3 marksOn the axes, sketch the intensity variation for the points W, X and Y.
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2 marksA 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.
The ultrasound transmitter is a coherent source.
Explain what is meant by the term coherent source.
4 marksExplain why the receiver detects regular rises and falls in the strength of the signals as it moves along the line AB.
3 marksCalculate the distance between the two slits.
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3 marksTwo 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.
With reference to the phase of the microwaves, deduce the magnitude of the detected signal at P and explain your reasoning.
5 marksDiscuss, with suitable calculations, what happens to the detected signal as the detector is moved from P to O.
2 marksThe source B is altered such that it emits waves that are 180° out of phase with source A.
Deduce the type of interference that now occurs at point P and explain your reasoning.
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2 marksA ray of light passes from air into a glass prism.
As the light ray passes through the prism, it emerges back into the air.
Calculate the critical angle from the glass to the air.
3 marksThe 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.
Calculate the refractive index of the gel.
2 marksA 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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4 marksThe 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.
Calculate the angle of incidence 
at the air–core boundary.
3 marksComplete the graph to show how the refractive index changes with radial distance along the line ABCD in Figure 2.
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3 marksThe diagram below shows an arrangement for observing the interference pattern produced by laser light passing through two narrow slits S1 and S2.
The distance S1S2 is d, and the distance between the double slit and the screen is D where D ≫ d, so angles θ and ϕ are small. M is the midpoint of S1S2 and it is observed that there is a bright fringe at point A on the screen, a distance fn from point O on the screen. Light from S1 travels a distance S2Y further to point A than light from S1.
The wavelength of light from the laser is 650 nm, and the angular separation of the bright fringes on the screen is 5.00 × 10−4 rad.
Calculate the distance between the two slits.
3 marksA bright fringe is observed at A.
(i) Explain the conditions required in the paths of the rays coming from S1 and S2 to obtain this bright fringe.
[2]
(ii) Determine an equation for the distance S2Y in terms of 
and 
.
[1]
4 marksDetermine an expression for
(i) 
in terms of , and
[2]
(ii) 
in terms of and 
.
[2]
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3 marksMonochromatic light from a single source is incident on two thin parallel slits.
The following data are available:
Distance from slits to screen = 4.5 m
Wavelength = 690 nm
Slit separation = 0.13 mm
The intensity, I of the light on the screen from each slit separately is I0.
Sketch, on the axis, a graph to show variation with distance p on the screen against the intensity of light detected on the screen for this arrangement.
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