P1.5 - Waves Flashcards
What do waves transfer and what DON’T they transfer?
Waves transfer energy without transferring matter.
What is the amplitude of a wave?
The amplitude of a wave is the distance from the rest position of a wave to the crest, or the top of the wave.
What is the amount of energy that a wave has dependent on?
The amount of energy a wave has depends on its amplitude.
What is meant by the wavelength of a wave?
The wavelength (λ) is the length of a “full cycle” of a wave, so from crest to crest.
What is the frequency of a wave?
The frequency is the number of complete waves produced by a source per second or the number of complete waves passing a point per second.
What is frequency measured in?
Frequency is measured in hertz (Hz).
1 Hertz is what?
1Hz is 1 wave per second.
How are transverse waves formed?
Transverse waves are formed by vertical vibrations (oscillations) from side to side.
What are some examples of transverse waves?
Light waves
Heat waves
Electromagnetic waves
Water ripples
Waves on strings
What are the properties of the oscillations of transverse waves?
In a transverse wave, the oscillations/vibrations are perpendicular (at 90 degrees) to the direction of energy transfer of the wave.
What are the sections of a longitudinal wave?
Longitudinal waves have compressions and rarefactions.
How do the particles in a longitudinal wave move?
The particles move backwards and forwards in the direction that the wave is travelling.
How do you work out the wavelength of a longitudinal wave?
The wavelength of a longitudinal wave is the distance between two compressions or two rarefactions.
What are some examples of longitudinal waves?
Sound waves
Ultrasound
P-Waves (seismic waves)
What are the properties of the oscillations of longitudinal waves?
In a longitudinal wave, the oscillations/vibrations are parallel to the direction of energy transfer of the wave.
What is the wave equation?
Speed (M/S) = Frequency (Hz) * Wavelength (M)
What is the speed of a wave independent of?
The speed is usually independent of the frequency or amplitude of the wave.
All waves can be…
All waves can be reflected, refracted, and diffracted, for when waves arrive at an obstacle their direction of travel will change.
When will the reflection of light be at different angles?
The reflection of light will be at different angles when light hits an uneven surface.
When will the reflection of light be at the same angle?
The reflection of light will be at the the same angle when light hits an even surface (like a mirror).
What is the “normal line”?
The “normal line” is an imaginary line that is perpendicular to the surface where light hits the surface (the point of incidence).
The angle of incidence is equal to what?
The angle of incidence = the angle of reflection.
What is a plane mirror?
A plane mirror is simply a flat mirror.
What are the properties of a reflected image?
The image is virtual - the image cannot be projected onto a screen (it is behind the mirror).
It is the same size as the original object.
It is upright.
The image is as far behind the mirror as the object is in front.
It is laterally inverted - the left and right sides are swapped.
What is the method for ray diagrams?
Draw a normal line.
Draw an incident ray from the top of the object to the mirror to hit the normal line and reflect.
Draw another normal line slightly below the original one.
Draw another ray from the object to the mirror, again reflecting off at the same angle.
Extend these lines behind the mirror - where the lines converge is where the virtual image is.
What do waves retain upon diffraction?
They retain their speed, frequency and wavelength.
What types of wave diffract?
All waves diffract - this means spreading out - when they pass through a gap.
When does maximum diffraction occur?
The gap must be about the same size as the wavelength for maximum diffraction.
When does little diffraction occur?
If the gap is much wider than the wavelength, there will be little diffraction.
When does diffraction only occur at the edges?
If the gap is a bit wider than the wavelength, there will be diffraction only at the edges.
What happens to the quality of diffraction if the gap that the waves travel through is the same size as the wavelength?
There is maximum diffraction.
What happens to the quality of diffraction if the gap that the waves travel through is much wider than the wavelength?
There will be little diffraction.
What happens to the quality of diffraction if the gap that the waves travel through is a bit wider than the wavelength?
There will be diffraction only at the edges.
When does light change direction?
Light changes direction when it changes speed.
When does light not change direction?
If a light wave hits a boundary/new substance along the normal line or “face on” its direction does not change.
What happens if a light wave travels along the normal?
If a light wave hits a boundary/new substance along the normal line or “face on” its direction does not change. \
The speed does, however.
When does a wave change direction?
If a wave meets a different medium at an angle, the wave changes direction.
When does light slow down and bend towards the normal?
Light may slow down and bend towards the normal line if it enters a denser material.
When does light bend away from the normal?
When light exits and enters the air, it will bend away from the normal as it enters the less dense material.
What is the order of the electromagnetic spectrum?
Radio
Microwaves
Infrared
Visible light
Ultraviolet
X-rays
Gamma Rays
What range do EM waves have with regards to wavelength?
EM waves vary in wavelength from around 10^-15 to 10^-4m.
At what speed to EM waves travel at in a vacuum?
EM waves travel at the speed of light in a vacuum (space).
EM waves with higher frequencies have what?
EM waves with higher frequencies have shorter wavelengths but have more energy.
What are radio waves used for?
Radio waves are used for radio transmissions and for terrestrial television (local transmitters).
What can long wavelength radio waves do?
Long wavelengths can diffract around the curved surface of the Earth, and around hills. This ensures that radio signals can be received even if the receiver is not in the line of light of the transmitter.
What can short-wave radio signals do?
Short-wave signals can be reflected off the ionosphere if they are in the line of sight.
What is the ionosphere?
The ionosphere is an electrically charged layer in the Earth’s upper atmosphere.
Can medium-wave radio wave signals reflect off of the ionosphere?
Medium-wave signals can reflect off of the ionosphere, depending on the atmospheric conditions and the time of day.
Can microwaves pass through the Earth’s atmosphere?
Microwaves can pass through the Earth’s atmosphere.
How do microwaves carry satellite TV signals?
The transmitter on the ground can transmit waves into space, where a satellite receiver can transmit the waves back down to Earth via a satellite dish.
Why are there concerns about mobile phones and their effect on our health?
Mobile phone calls transmit as microwaves between the handset and the transmitter.
The body may absorb microwaves and fry the cells as a result, causing health issues.
Why should we not be worried about mobile phones and their effect on our health?
The amount of energy the body may absorb is minimal and therefore negligible.
How can infrared waves control appliances?
Infrared waves can emit different patterns of infrared waves to send commands to an appliance, such as a TV.
How do optical fibres work?
Optical fibres can carry data over long distances by carrying a signal as pulses of light or IR.
They will reflect this signal off the sides of a narrow core from one end of the fibre to another.
What is visible light used for?
Visible light is used for vision and photography.
What are sound waves caused by?
Sound waves are caused by vibrating objects.
When do sound waves travel faster?
They travel faster in solids than in liquids, and faster in liquids than in gases.
Why can’t sound travel in a vacuum?
Sound cannot travel in a vacuum because there are no particles.
How are the mechanical vibrations of sound passed through the surrounding medium?
The mechanical vibrations are passed through the surrounding medium as a series of compressions.
What are echoes?
Echoes are reflected sound waves.
Why can sound echo?
Sound can echo because the sound can reflect, refract, etc.
Describe the properties of high frequency sound waves.
High frequency sound waves are high pitched and have a short wavelength.
Describe the properties of low frequency sound waves.
Low frequency sound waves are low pitched.
The bigger the amplitude…
The bigger the amplitude, the louder the sound.
What happens when a source moves towards an observer?
When a source moves towards an observer, the observed wavelength decreases and the frequency increases, along with the pitch.
What happens when a source moves away from a observer?
When a source moves away from an observer, the observed wavelength increases and the frequency and the pitch decrease.
Under the Doppler Effect, what remains the same?
The speed of the waves remains the same.
Light that is further away from us has a longer what?
Light that is further away from us has a longer wavelength.
Objects that are further away from us appear…
Objects that are further away from us appear red.
Objects that are closer to us appear…
Objects that are closer to us appear blue.
Why do galaxies have a greater red-shift?
Galaxies are moving away from us.
What is the Big Bang Theory?
The universe initially began from a singular point and the matter and energy expanded from that point (after being compressed).
What is CMBR?
CMBR (Cosmic Microwave Background Radiation) is low frequency EM radiation that was present as the beginning of the whole universe.
Why is CMBR now low frequency waves?
CMBR is low frequency as it has dropped in frequency as the universe cooled.
