Waves Flashcards
What can we use waves for?
Transmitting energy and information
What is the direction of travel of the wave the same as?
The direction in which the wave transfers energy
Describe a transverse wave
The oscillation (vibration) of the particles is perpendicular to the direction in which the wave travels
Describe a lonitudinal wave
The oscillation of the particles is parallel to the direction of the wave
Describe electromagnetic waves
- Can travel through a vacuum
- There are no particles moving, they are oscillations in electric and magnetic fields
- Are transverse
Describe mechanical waves
- E.g. waves on springs and sound waves
- Travel through a medium (substance)
- Can be transverse or longitudinal
Describe sound waves
- Vibrations in the air/other media
- These are eventually picked up by your ear, producing the sound
- Longitundial
Aside from transverse and longitundal, what types of waves are there (and are they transverse or longitundinal)?
- Electromagnetic - Transverse
- Mechanical - Either
- Sound - Longitundinal
Do longitudinal waves have an amplitude?
No
What is the amplitude of a wave?
The height of the wave crest or the depth of the wave trough from the position at rest
Greater amplitude = more energy
Defines the loudness of a sound wave (think of amps)
Complete the sentence:
The greater the amplitude of a wave…
…the more energy a wave has
What is the wavelength of a wave?
The distance from one crest to the next, or from one trough to the next
Measured in metres
What is the frequency of a wave?
The number of complete waves passing a set point per second
Measured in hertz (Hz) which is equivalent to per second
What is the wavelength of a longitudinal wave?
The distance from the middle of one compression/rarefaction to the next
(Instead of from one peak/crest/trough)
What is the frequency of a longitudianl wave?
The number of compressions passing a point per second
(As opposed to crests/troughs/peaks. Still complete waves)
What is meant by a plane mirror?
A flat mirror
When drawing a ray diagram, what should you always remember?
To draw the normal!
Where is the normal line drawn?
Perpendicular to the mirror/medium at the point where the incident ray hits the mirror
What does the law of reflection state?
That the angle of incidence is equal to the angle of reflection
What is the angle of incidence/reflection?
The angle between the incident/reflected ray and the normal
I.e. Not the medium/mirror!
Describe the image formed on a mirror
- Same size as the object (not magnified/diminshed)
- Upright
- Same distance behind the mirror as the object is in front
- Virtual
What is a real image?
One that can be formed on a screen becayse the rays of light actually pass through it
What is a virtual image?
Cannot be formed on a screen because the rays of light only appear to pass through it
What changes when a wave crosses a boundary between different substances?
The speed and wavelength
The frequency stays the same
The wave also changes direction due to the change in speed
Refraction is a property of what kind of wave?
All kinds
What does the change in the speed of a wave cause?
A change in direction (refraction)
What happens when light enters a more dense substance?
It slows down and bends towards the normal
What happens when light enters a less dense substance?
It speeds up and bends away from the normal
If light is travelling along the normal and enters a different substance, what will happen?
It will not change direction
What is dispersion?
- Different colours of light have different wavelengths
- These are refracted by slightly different amounts when entering a different substance
- When a ray of white light is shone onto a triangular prism we can see this because a spectrum is produced
- Violet light is refracted the most, red light the least
Why does light split up into different colours when it passes through a triangular prism?
Because the different wavelengths of light are refracted by different amounts
What types of waves is diffraction a property of?
All waves
What is diffraction?
The spreading out of waves when they pass through a gap/around an obstacle
It is most noticable if the wavelength of a wave is about the same size as the gap/obstacle
Why don’t we often observe the diffraction of light during everyday life?
Because the wavelength of light is very short
Why might someone get poor TV/mobile signal if they live in a hilly area?
- These signals are carried by radio waves
- These might be blocked by a hill
- Radio waves will be diffracted around the hill
- If they do not diffract enough, the signal will not reach the reciever aerial and will be poor
Draw a diagram showing diffraction through a narrow and wide gap
What causes sound?
Mechanical vibrations in a substance. It travels as waves
What can sound travel through and at what speed (roughly)?
Can travel through solids, liquids, and gases.
It travels fastest in solids and slowest in gases
In other words, sound needs a medium through which to travel
What can sound not travel through and how do we know this?
It cannot travel through a vacuum
This can be tested by listening to a ringing bell in a ‘bell jar’. If the air is pumped out of the jar, the sound fades away.
What range of frequencies of sound can be heard by the human ear, and how does age affect this?
20Hx to 20,000Hz
The ability to hear higher frequencies declines with age
What are the reflections of sound waves called?
Echoes
What affects how/if echoes are produced?
- Only hard, flat surfaces such as flat walls and floors reflect sound
- Soft things like carpets, curtains, and furniture absorb sounds
- An empty room will sound different once soft furnishings etc. are put into it/removed
Where does the refraction of sound waves take place?
At the boundaries between layers of air at different temperatures
What does the pitch of a note/sound depend upon?
The frequency of a wave
The higher the frequency, the higher the pitch
What does the loudness of a note/sound depend upon?
The amplitude of a wave
The higher the amplitude, the louder the sound
This is because the wave carries more energy
(Think of amps)
What does an oscilloscope show?
Waves + the differences in waveform (comparing waves)
What can tuning forks and signal generators be used to produce?
‘Pure’ waveforms
What does the quality of a note depend upon?
The waveform
Why do different instruments not sound the same?
Because they produce different waveforms
How do musical instruments produce sound?
- Vibrations created in an instrument when it is played produce sound waves
- In some instruments, e.g. saxophones, a column of air vibrates
- In others, e.g. a violin, a string vibrates
- Some instruments vibrate when they are struck, e.g. a xylophone
