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3 Waves - iGCSE Physics Edexcel

Terms in this set (29)

3.1 use the following units: degree (°), hertz (Hz), metre (m), metre/second (m/s) and second (s)
angle = degree (°)
frequency = hertz (Hz)
wavelength = metre (m)
velocity = metre/second (m/s)
time = second (s)
3.2 explain the difference between longitudinal and transverse waves
Transverse
-Vibrations perpendicular to energy transfer
-All of EM waves are transverse

Longitudinal
-Vibrations parallel to energy transfer
-Sound waves
3.3 know the definitions of amplitude, wavefront, frequency, wavelength and period of a wave
Wavelength is the distance from a point on one wave to the same point on the next wave.
IE peak to peak

Amplitude of a wave is its height, measured from the middle of the wave to its top

Wavefront is a way of picturing waves from above: Each wavefront is used to represent a single wave.

The frequency of a wave is the number of waves passing a point every second
Waves per second
Measured in Hertz (HZ)

Timeperiod is time taken for a wave to pass through a point
Measured in seconds
3.4 know that waves transfer energy and information without transferring matter
-When a wave travels between two points, no matter actually travels with it:
-The points on the wave simply vibrate back and forth about fixed positions.
-There is energy transferred due to vibrations
3.5 know and use the relationship between the speed, frequency and wavelength of a wave: wave speed = frequency × wavelength v = f × λ
wave speed (m/s) = frequency (Hz) x Wavelength (m)
v = f × λ
3.6 use the relationship between frequency and time period:
Frequency (Hz) = 1/ Time Period (s)
f = 1/T
3.7 use the above relationships in different contexts including sound waves and electromagnetic waves
wave speed (m/s) = frequency (Hz) x Wavelength (m)
v = f × λ

Frequency (Hz) = 1/ Time Period (s)
f = 1/T
3.8 explain why there is a change in the observed frequency and wavelength of a wave when its source is moving relative to an observer, and that this is known as the Doppler effect
-When source of wave is moving, the waves may be squashed or stretched

-Wavelength of waves in front of source decrease
-Frequency and pitch increase

-Wavelength of waves behind source increase
-Frequency and pitch decrease
3.9 explain that all waves can be reflected and refracted
Relfection
-When waves hit an object, such as a barrier, they can be reflected
-Angle of incidence = angle of reflection
i = r

Refraction
-When waves enter a different medium, their speed can change.
-Wavelength can increase or decrease
-Direction changes

If the waves slow down:
-the waves will bunch together causing wavelength to decrease. -Waves travel closer to the normal

If waves speed up:
-Waves spread out, causing the wavelength to increase
-Waves turn away from the normal
3.10 know that light is part of a continuous electromagnetic spectrum that includes radio, microwave, infrared, visible, ultraviolet, x-ray and gamma ray radiations and that all these waves travel at the same speed in free space
All electromagnetic waves have the following properties:
-Transfer energy
-Are transverse waves
-Travel at the speed of light in a vacuum
-Can be reflected and refracted
3.11 know the order of the electromagnetic spectrum in terms of decreasing wavelength and increasing frequency, including the colours of the visible spectrum
In order of increasing frequency and decreasing wavelength:
Radio Waves - Highest wavelength. Lowest frequency
Microwaves
Infrared (IR)
Visible Light
Ultraviolet (UV)
X - Rays
Gamma Rays - Highest frequency. Lowest wavelength

Light=ROYGBIV
Red - Highest wavelength. Lowest frequency
Orange
Yellow
Green
Blue
Indigo
Violet - Highest frequency. Lowest wavelength
3.12 explain some of the uses of electromagnetic radiations, including: • radio waves: broadcasting and communications • microwaves: cooking and satellite transmissions • infrared: heaters and night vision equipment • visible light: optical fibres and photography • ultraviolet: fluorescent lamps • x-rays: observing the internal structure of objects and materials, including for medical applications • gamma rays: sterilising food and medical equipment.
radio waves: broadcasting and communications

microwaves: cooking and satellite transmissions

infrared: heaters and night vision equipment

visible light: optical fibres and photography

ultraviolet: fluorescent lamps

x-rays: observing the internal structure of objects and materials, including for medical applications

gamma rays: sterilising food and medical equipment.
3.13 explain the detrimental effects of excessive exposure of the human body to electromagnetic waves, including: • microwaves: internal heating of body tissue • infrared: skin burns • ultraviolet: damage to surface cells and blindness • gamma rays: cancer, mutation and describe simple protective measures against the risks
Microwave: Heat damage to organs

Infrared: Skin burns

Visible light: bright lights cause eye damage

UV: kills and mutates cells

X rays: Kills and mutates cells, causes cancer

Gamma rays: Kills and mutates cells, causes cancer
3.14 know that light waves are transverse waves and that they can be reflected and refracted
Light are part of EM spectrum
All EM waves can undergo reflection and refraction.
3.15 use the law of reflection (the angle of incidence equals the angle of reflection)
angle of incidence = angle of reflection
i = r
3.16 draw ray diagrams to illustrate reflection and refraction
REFLECTION
When an object is placed in front of a mirror, an image of that object can be seen in the mirror.

Light from the object hits the mirror, reflecting from it.
When it does so, the angle of incidence = the angle of reflection
To an observer, the reflected rays appear to have come from the right hand side of the mirror.
An image of the object will appear where these two virtual rays cross.

REFRACTION
As the light enters the block it bends towards the normal line.

When it leaves the block it bends away from the normal line.
3.17 practical: investigate the refraction of light, using rectangular blocks, semi-circular blocks and triangular prisms
Method:
Place the glass block on a sheet of paper, and carefully draw around the block using a pencil.

Take a ray box and carefully aim the box so that a single ray of light passes through the block.
Using a pencil, mark some points along the path of the ray:
Before it reaches the block;
Where it hits the block;
Where it leaves the block;
After it has left the block.

Now remove the block from the paper and, using a ruler and pencil, draw straight lines connecting points: a and b; b and c; c and d. The resulting line will show the path of the ray.

Replace the block within its outline and repeat the above process for a ray striking the block at a different angle.
3.18 know and use the relationship between refractive index, angle of incidence and angle of refraction: sin i / sin r
Snell's law
Refractive index= sin (angle of incidence)/ sin (angle of refraction)

n = sin i / sin r
3.19 practical: investigate the refractive index of glass, using a glass block
Place the glass block in the centre of a piece of paper and draw around it in pencil.

Remove the block and then, using a protractor, draw a line crossing the longest edge of the block (about midway down) at 90 degrees (the normal line).

Using a protractor and ruler draw other lines, crossing this point, at 10 degree intervals (relative to the normal) going up to 70 degrees maximum.
These angles will form the angle of incidence (the independent variable) for this experiment.

Replace the block and then, using a ray box, shine a ray of light along the first of the above lines (10 degrees).

Use a pencil to mark the point at which the ray emerges from the other side of a block.

Repeat the above two steps for the other lines.
Once complete, remove the block and then use a pencil and ruler to draw some lines linking the point of entry of each ray to the point of exit.

Using a protractor, measure the angle between each of the above lines and the normal, recording each result in a table along with the appropriate angle of incidence.

Repeat the above procedure three times and take averages of each of the results.

To find the refractive index of the block:
Plot a graph of sin i (y-axis) against sin r (x-axis).
The refractive index is equal to the gradient of the graph.
3.20 describe the role of total internal reflection in transmitting information along optical fibres and in prisms
-Sometimes, when light is moving from a denser medium towards a less dense one, light is fully reflected
-Called TIR, and is used to reflect light
-Used to reflect light along optical fibres, allowing the high speed transmission of data on the internet.

-Optical fibre is cheaper than copper wires
-Can carry more information than copper wire of same size
3.21 explain the meaning of critical angle c
-The angle of incidence which produces an angle of refraction of 90 degrees, or reflection
-When the angle of incidence is greater than the critical angle, TIR occurs
-Only occurs from a high refractive index medium to a low refractive index medium.
3.22 know and use the relationship between critical angle and refractive index: sin c = 1 / n
Critical angle of a material is related to refractive index.

sin c = 1 / n

n = 1 / sin c
3.23 know that sound waves are longitudinal waves which can be reflected and refracted
Sound waves consist of vibrating air molecules.
-Longitudinal wave.

As with all waves, sound waves can be reflected and refracted.
3.24P know that the frequency range for human hearing is 20-20 000 Hz
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3.25P practical: investigate the speed of sound in air
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3.26P understand how an oscilloscope and microphone can be used to display a sound wave
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3.27P practical: investigate the frequency of a sound wave using an oscilloscope
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3.28P understand how the pitch of a sound relates to the frequency of vibration of the source
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3.29P understand how the loudness of a sound relates to the amplitude of vibration of the source
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