National 5 Waves Flashcards
Factual Recall
1.1 What does a wave transfer?
A wave transfers Energy
1.2 Explain the difference between a transverse and longitudinal wave.
In a transverse wave the medium oscillates at right angles to the direction of energy transfer.
In a longitudinal wave the medium oscillates parallel to the direction of energy transfer.
1.3 Classify examples of transverse and longitudinal waves.
Longitudinal: Sound
Transverse: Water, Light, Radio Waves, All Electromagnetic Waves
1.4 Define Frequency
Frequency (f) is the number of waves per second.
It is measured in Hertz (Hz).
1.4 Define Wavelength
Wavelength (greek letter lambda λ) is the length of one complete wave, often measured between successive crests or troughs.
It is measured in metres (m).
For example, A in the image.
1.4 Define Period
Period (T) is the time for one complete wave.
It is measured in seconds (s).
1.4 Define Amplitude
Amplitude (A) is the height of a wave from the middle (line of zero disturbance) to the top (crest), or from the bottom (trough) to the middle.
It is measured in metres (m).
For example, D in the attached image.
1.4 Define Speed
Speed (v) is the distance travelled per unit of time by a wave.
It is measured in metres per second (ms-1).
1.4 Define a Crest
A Crest is the highest point of a wave.
For example, B in the attached image.
1.4 Define a Trough
A Trough is the lowest point of a wave.
For example, C in the attached image.
1.5 f = 1/T
(Define symbols and units)
f - frequency (Hz)
T - period (s)
1.5 Example
A bat emits ultrasounds with a period of 23 µs. Calculate the frequency of the ultrasound.
T = 23 µs = 23 x 10<sup>-6</sup> s f = ?
f = 1/T f = 1/23 x 10<sup>-6</sup> f = 4.35 x 10<sup>4</sup> Hz
1.5 f = N/t
(Define symbols and units)
f - frequency (Hz)
N - Number of waves (no units)
t - time (s)
1.5 Example
A siren produces 26,400 waves per minute.
Calculate their frequency.
N = 26,400 t = 1 min = 60 s f = ?
f = N/t f = 26,400/60 f = 440 Hz
1.6 v = f λ
(Define symbols and units)
v - speed (ms-1)
f - frequency (Hz)
λ - wavelength (m)
1.6 Example
Some water waves have a wavelength of 2 m and a frequency of 6 Hz.
Calculate their speed.
v = ? f = 6 Hz λ = 2 m
v = fλ v = 6 x 2 v = 12 ms<sup>-1</sup>
1.6 d = vt
(Define symbols and units)
d - distance (m)
v - speed (ms-1)
t - time (s)
1.6 Example
A cannon is 170 m away.
The sound from the cannon firing takes 0.5 s to reach you.
Use this to calculate a value for the speed of sound in air.
v = ? t = 0.5 s d = 170 m
d = vt
170 = v x 0.5
v x 0.5 = 170
v = 170/0.7
v = 340 ms-1
1.6 Example
An ultrasound scanner detects an echo from a baby’s head after 0.12 ms.
How far away is the baby’s head?
(Take the speed of sound in tissue to be 1500 ms-1)
Don’t forget that in an echo problem the echo has to travel there and back.
v = 1,500 ms<sup>-1</sup> t = ½ x 0.12 ms = ½ x 0.12 x 10<sup>-3</sup> = 6 x 10<sup>-5</sup> s (half for there only) d = ?
d = vt
d = 1,500 x 6 x 10-5
d = 0.09 m
The baby’s head is 0.09 m away.
1.7 What is meant by diffraction?
Diffraction is when a wave bends round an obstacle or through a gap.
1.7 What are the practical limitations of diffraction?
If an object is small compared to the wavelength, the wave will bend round the object and it cannot be detected.
If a gap is small compared to the wavelength, significant diffraction occurs leading to semicircular wavefronts.
1.8 State the effect of wavelength on diffraction.
Longer wavelengths diffract more than shorter wavelengths.
2.1 What is meant by the electromagnetic spectrum?
The electromagnetic spectrum is a family of waves with similar properties.
They can all travel through a vacuum.
2.1 List the electromagnetic spectrum in order of increasing wavelength.
Gamma, X-Rays, Ultraviolet, Visible, Infrared, Microwaves, Radio Waves
2.2 Give one typical source, detector and application for Gamma Rays
Source: Nuclear Decay, Cosmic Rays, Stars
Detector: Geiger-Muller Tube, Photographic Film
Applications: Treating Cancer (Radiotherapy), Tracers to diagnose illness
2.2 Give one typical source, detector and application for X-Rays
Source: Man-made sources, Stars
Detector: Photographic Film
Applications: Diagnosing broken bones
2.2 Give one typical source, detector and application for Ultraviolet
Source: Ultra-Hot objects, Electrical discharges/sparks, Stars
Detector: Photographic Film, Chemical Flourescence
Applications: Tanning Beds
2.2 Give one typical source, detector and application for Visible Light
Source: Very-Hot objects (lamps), Electrical discharges/sparks, Stars
Detector: Photographic Film, Photodiode, Charge-Coupled Device (CCD), Human Retina
Applications: Seeing
2.2 Give one typical source, detector and application for Infrared
Source: Hot objects, Stars
Detector: Photographic Film, Photodiode
Applications: Optical fibre communication, Remote controls, “Night” vision
2.2 Give one typical source, detector and application for Microwaves
Source: Electrical circuits, Stars
Detector: Diode Probe Receiver
Applications: Cooking, Mobile Phone signals
2.2 Give one typical source, detector and application for Radio Waves
Source: Electrical circuits, Stars
Detector: Aerial
Applications: Mobile Phone signals, Television signals
2.3 Comment on the speed of Electromagnetic Waves
All Electromagnetic Waves travel at the same speed, which is the speed of light (3 x 108 ms-1).
2.3 Example
Microwaves have a frequency of 9.4 GHz. Calculate their wavelength.
v = 3 x 10<sup>8</sup> ms<sup>-1</sup> (Since EM Wave) f = 9.4 GHz = 9.4 x 10<sup>9</sup> Hz λ = ?
v = fλ
3 x 108 = 9.4 x 109 x λ
9.4 x 109 x λ = 3 x 108
λ = 3 x 108/9.4 x 109
λ = 0.032 m
2.3 Example
Radio Waves takes 1.28 seconds to travel from the moon to the earth. How far away is the moon?
v = 3 x 10<sup>8</sup> ms<sup>-1</sup> (since EM Wave) t = 1.28 s d = ?
d = vt
= 3 x 108 x 1.28
d = 3.84 x 108 m
2.3 Example
The sun is 1.5 x 1011 m away.
How long does it take light to travel from the sun to the Earth?
v = 3 x 10<sup>8</sup> ms<sup>-1</sup> (since EM Wave) d = 1.5 x 10<sup>11</sup> m t = ?
d = vt
1.5 x 1011 = 3 x 108 x t
3 x 108 x t = 1.5 x 1011
t = 1.5 x 1011/3 x 108
t = 500 s
3.1 & 3.2 What is meant by refraction
Refraction is the change in speed that occurs when a wave changes from one medium to another. Wavelength also changes and usually direction (except when the angle of incidence is zero).
3.3 Identify correctly the angle of incidence, angle of refraction and normal in ray diagrams showing refraction.
The normal is an imaginary line at right angle to the surface where a ray strikes. (The dashed grey vertical line in the image)
The angle of incidence is the angle between the ray striking the surface and the normal. (P in the image)
The angle of refraction is the angle between the ray leaving the surface and the normal. (Q in the image)
