P1.5 Waves Flashcards
What is a wave?
A vibration that transfers energy without transferring any matter
How do waves transfer energy?
By making the particles that it is travelling through vibrate
What does a wave on axes show?
The displacement of one particle from its rest position as the wave moves over time/distance
What do crests and troughs show on a displacement wave graph?
They are the peaks of the wave, the crests show the maximum displacement from the particle’s rest position and the troughs show the minimum displacement
What is the amplitude of a wave?
The displacement from the rest position to a crest or a trough
What is the wavelength of a wave?
The length of a full cycle of the wave e.g. the distance from crest to crest
What is the frequency of a wave?
The number of complete waves passing a certain point per second or the number of waves produced by a source per second
What is frequency measured in?
In hertz (Hz), 1 Hz is 1 wave per second
What is the equation for the speed of a wave?
v = f x λ // Speed in m/s = frequency in Hz x wavelength in m
In what direction do waves transfer energy?
In the same direction as they travel
What is a transverse wave?
Waves which have vibrations that are perpendicular (90°) to the direction of energy transfer of the wave
What are three examples of transverse waves?
Light and all other electromagnetic waves, ripples on water and waves on strings
What are areas of compression in a longitudinal wave?
Where particles are bunched together
What are areas of rarefaction in a longitudinal wave?
Where particles are spread out
What is a longitudinal wave?
A wave that has vibrations that are parallel to the direction of energy transfer of the wave
What are three examples of longitudinal waves?
Sound waves, ultrasounds and some earthquake waves called seismic waves
What do mechanical waves need in order to travel?
They need a medium to travel in - they can’t travel in a vacuum
Are mechanical waves transverse or longitudinal waves?
They can be either
What are examples of mechanical waves? (3)
Water waves, sound waves and waves in springs
How can waves change their direction of travel when they arrive at an obstacle or meet a boundary? (3)
By reflection, refraction or diffraction
What is reflection?
When a wave meets a boundary between two media it can bounce back (it took an L, lol xD ROFL)
What does reflection allow humans to do?
It allows us to see objects - the reflection of light bounces of objects and into our eyes
What happens when light is reflected form a smooth, even surface?
The light is reflected at the same angle and you get a clear reflection
What happens when light is reflected from an uneven surface?
The light is reflected off at different angles
What is refraction?
When a wave changes direction as it crosses a boundary between media
What is the ‘normal’ of a boundary?
An imaginary line that’s perpendicular (90°) to the boundary at the point of incidence (where the wave hits the boundary)
How do waves need to meet the boundary in order to be refracted?
Waves are only refracted if they meet the boundary at an angle to the normal - waves travelling along the normal are not refracted
What is diffraction?
When waves spread out at
When do waves diffract?
At the edges when they pass through a gap or pass an obstacle
What does the amount of diffraction depend on?
The size of the gap relative to the wavelength of the wave - the narrower the gap, or the longer the wavelength, the more the wave spreads out
Why does sound need a large gap to diffract?
Because it has a long wavelength
Why does light need a small gap to diffract?
Because it has a short wavelength
What are electromagnetic waves a group of?
Transverse waves
What is the electromagnetic spectrum?
A continuous spectrum of all possible wavelengths of electromagnetic waves
What happens when you go from left to right in the EM spectrum? (2)
Frequency and energy increase
What happens when you go from right to left in the EM spectrum?
Wavelength increases
What important things are there to know about EM waves? (3)
They vary in wavelength from around 10⁻¹⁵m to 10⁴m, they all travel at the same speed 3 x 10⁸m/s in a vacuum, and EM waves with higher frequencies have shorter wavelengths
Radio waves are an example of an EM wave, what are they used for? (2)
For radio and TV signals
What happens when a long radio wave comes into contact with the curvature of the earth?
Long-wave radio can be transmitted and received halfway round the world because the wavelengths diffract (bend) around the curved surface of the earth
What allows long-wave radio to be received from somewhere which isn’t in line of sight of the transmitter?
Long radio waves can diffract around hills, into tunnels and much more - this allows the radio waves to reach receivers which aren’t in the line of sight of the transmitter
Short-wave radio signals don’t diffract around the earth but can still be received at large distances, why?
Because they reflect between the earth and the ionosphere (this is similar for medium-length signals, but they depend on the atmospheric conditions and the time of day)
What is the ionosphere?
An electrically charged layer in the Earth’s upper atmosphere
What waves do TV and FM radio transmit? How does this affect you as a viewer?
They have very short-wave radio signals - which means you need to be in direct sight of transmitter to get reception
Why are microwaves used for communication to and from satellites?
Because some microwaves can easily pass through the Earth’s atmosphere without being reflected, refracted, diffracted or absorbed - so they can reach satellites
What happens when a microwave reaches a satellite?
Once the satellite has received the signal, it transmits the signal back to earth but in a different direction where it’s received by a satellite dish on the ground
How do mobile phones use microwaves?
They use microwaves to send signals between your phone and the nearest transmitter
What are remote-sensing satellites used for? And how do they carry out this particular function?
They use microwaves to monitor the Earth from space - they can be used to ‘see’ through the clouds and monitor oil spill, track the movement of icebergs etc.
What health concerns are there with using microwaves?
Some wavelengths of microwaves are absorbed by water molecules and heat them up - water molecules are in cells in human bodies which, when heated, can lead to cancer
What are infrared waves used in? (2)
Remote controls and signals in optical fibres
How do wireless remote controls use infrared waves to send commands to an appliance?
They emit different patterns of infrared waves to send different commands to an appliance e.g. a TV
What are optical fibres?
Very thin wires with a glass or plastic core that can be used to transmit signals of infrared or visible light
How are signals carried in optical fibres?
They are carried as pulses of light or infrared radiation and is reflected off the sides of a very narrow core from one end of the fibre to the other
Why are optical fibres used in phone lines?
Because they can carry data over long distances very quickly
What is infrared radiation also known as?
Heat radiation
What gives out infrared waves?
All hot objects - the hotter the object the more infrared waves it gives out
What can infrared radiation be used for in cameras?
They can be used to monitor temperatures - infrared cameras can create an image showing temperature variations and the images can be colour coded to show different amount of IR
How do cameras use a lens?
The lens in a camera is used to focus visible light onto a light-sensitive film or electronic sensor
What does the lens aperture control?
It controls how much light enters the camera
What does the shutter speed in a camera determine?
How long the film or sensor is exposed to the light
What does varying the aperture and shutter speed of a camera allow a photographer do?
It allows them to capture as much or as little light as they want in their photograph
How do you draw the normal when drawing a simple reflection from a boundary?
The normal - which is perpendicular to the boundary at the point the incidence wave hits (it is also drawn as a dashed line)
What is the angle of incidence?
The angle between the path of the incident wave and the normal
What is the angle of reflection?
The angle between the path of the reflected wave and the normal
What is the law of reflection?
Angle of incidence = angle of reflection
What is an image?
A picture of an object formed by light from the object
What is a virtual image?
An image that is formed when light rays appear to appear to have come from a point that they don’t actually pass through
What happens when you put up a screen where a virtual image appears to meet?
The image will not appear on the screen, because the light rays forming it aren’t actually there
What does a virtual image look like?
Upright and laterally inverted
What is a ray diagram?
A diagram that shows how the rays of light from an object form an image when reflected (or refracted)
What are sound waves?
Mechanical vibrations (so they travel through the surrounding medium) caused by vibrating objects
What type of wave are sound waves?
They are a type of longitudinal wave which move as a series of compressions
How do people hear sound?
When the sound waves travel through someone’s ear and reach their eardrum
From slowest to fastest, what do sound waves move fastest though?
Gas, liquid and solid
Why can’t sound travel in space?
Because it’s mostly a vacuum so there are no particles to vibrateW
What is an echo?
When sound waves reflect off of a hard flat surface, there is a delay between the original sound and the reflect sound waves because they have to travel further thus taking longer to reach the ear
What happens when sound waves enter different media? e.g. from air to water
They refract (change direction)
What does the pitch of a sound depend on?
The frequency of the sound wave - high frequency sound waves are high pitched, and low frequency sound waves are low pitch
What does the loudness of a sound depend on?
The amplitude - the bigger the amplitude, the louder the sound
What is the Doppler effect?
When you move towards or away from something that emits waves, the wavelengths and frequencies of the waves seem different
What happens to the frequency and wavelength as you move towards a wave source?
The frequency will seem higher and the wavelength shorter
What happens to the frequency and wavelength as you move away from a wave source?
The frequency will seem lower and the wavelengths longer
What waves does the Doppler effect affect?
Both longitudinal and transverse waves
What is the Doppler effect of a light source known as?
Red-shift
What happens to a light source as it moves away from us?
The frequency of the light gets lower and shifts towards the red end of the spectrum - making the light appear redder than it actually is
What happens to a light source as it moves away from us?
The frequency of the light gets higher and shifts towards the blue end of the visible light spectrum - making the light source appear bluer than it actually is, this is known as blue-shift
What is shown on the absorption spectra?
A spectrum which shows what frequency of light each element absorb - a spectrum with dark lines in it is called a line absorption spectrum
What do we see when comparing the absorption spectra of Earth and the absorption spectra from a distant galaxy?
We see the elements absorbing light waves with lower frequencies than they should be - they have shifted towards the red end of the spectrum (red shift)
What does the red shift of galaxies show?
That they are moving away from us very quickly
How does the red-shift of galaxies change compared to their distance from earth?
The further the galaxy, the more red-shift and the faster they are moving away from us
What theory explains why distant galaxies are moving away from us?
Scientists believe a big explosion would have caused these galaxies to originally begin to move - the Big Bang theory
What does the Big Bang theory state?
That all matter and energy in the universe was once compressed into a very small space - which then exploded, and the universe has been expanding ever since
How can we estimate the age of the universe?
By using the current rate of expansion
What is another theory of how the universe began?
The Steady State theory
What is cosmic microwave background radiation (CMBR)?
Low-frequency electromagnetic radiation coming from all over the universe have been discovered, this is mostly found in the form of microwaves (CMBR)
Why is the Big Bang theory greatly accepted?
Because it explains CMBR
How does the Big Bang theory explain CMBR?
Just after the Big Bang the universe was extremely hot, and everything was emitting very high frequency radiation - but as the universe expanded, it has and this radiation has dropped in frequency and is now found as microwaves
What problems are there with the Big Bang theory? (2)
It doesn’t explain how the explosion started in the first place and it doesn’t explain the what conditions were like pre-explosion
