waves Flashcards
What is a transverse wave?
In transverse waves, the oscillations (vibrations) are perpendicular to the direction of energy transfer.
What is a longitudinal wave?
In longitudinal waves, the oscillations (vibrations) are parallel to the direction of energy transfer.
What is the amplitude of a wave?
The amplitude is the height of a wave.
on a graph, from centre line to crest
What is the wavelength?
The wavelength is the length of one complete wave cycle.
What is the crest of a wave?
The crest is the top of a wave.
What is the trough of a wave?
The trough is the bottom of a wave.
What is the frequency of a wave?
The frequency is the number of waves that pass one point each second.
What is the period of a wave?
The period is the time it takes for one wave to pass a point.
What is the wave speed?
Wave speed is the speed at which energy is transferred through a medium.
How do you calculate wave speed?
wave speed (m/s) = frequency (Hz) x wavelength (m)
What three things could happen to a wave at a boundary between two materials?
Waves can either be reflected, absorbed or transmitted at a boundary between two materials.
What is the normal?
The normal is perpendicular to the boundary which reflects, absorbs or transmits the wave.
What is the angle of incidence?
The angle of incidence is the angle between the incoming ray and the normal.
This is numerically equivalent to the angle of reflection.
What is the angle of reflection?
The angle of reflection is the angle between the normal and the reflected ray.
This is numerically equivalent to the angle of incidence.
What is diffuse reflection?
diffuse reflection:
- reflection of light off of a rough surface
- the normal is different for each position on the material, so the angles of incidence and reflection are different at each position
- there is not a clear reflection
What is specular reflection?
specular reflection:
- reflection of light off of a smooth surface
- the normal is always the same
- clear reflection
What is refraction?
Refraction is when a wave changes direction at a boundary between two materials.
What affects the level of refraction for a wave?
How much a wave is refracted depends on how much the wave speeds up or slows down, which usually depends on the density of the material. The higher the density, the slower the wave travels.
What happens if a wave hits a boundary along the normal?
If a wave hits a boundary along the normal, the wave is not refracted and continues in that direction.
What is the optical density?
The optical density of a material is how quickly light can travel through it. The more optically dense an object is, the more the refracted ray bends towards the normal.
Are sound waves longitudinal or transverse?
Sound waves are longitudinal. They cause the particles to vibrate back and forth.
How do sound waves travel through a solid?
Sound waves can travel through solids by causing vibrations in the solid. This only works over a limited frequency range.
How do sound waves cause humans to hear sound?
Within the ear, sound waves cause the ear drum and other parts to vibrate, which causes sound.
What is the restriction of typical human hearing?
The typical restriction of human hearing is 20Hz - 20,000Hz (20kHz)
Why do sound waves travel faster through solids?
Sound waves travel faster through solids as the particles are closer together, so the vibrations are passed on easier and quicker.
Can wavelength change across different materials? Why (not)?
Wavelength can change across different materials as the wave speed can change, and wave speed = frequency x wavelength.
Can frequency change across different materials? Why (not)?
Frequency cannot change across different materials as that would mean creating or destroying waves, which is impossible.
Which aspect of the wave affects how loud or quiet a sound is?
The larger the amplitude of the wave, the louder the sound.
Which aspect of the wave affects how high or low pitched a sound is?
The higher the frequency of the wave, the higher the pitch of the sound.
How can sound waves be viewed?
Sound waves can be viewed by connecting a microphone to a cathode ray oscilloscope.
What is ultrasound?
Ultrasound is a wave with a frequency over 20kHz, which is above the average human hearing limit.
How can ultrasound waves be used to find images for industrial or medical purposes?
Ultrasound can be emitted from an emitter and a detector in one. This calculates the time taken for the reflections to reach the detector, which can be used to determine how far away a boundary is. This distance is calculated with distance = speed x time.
What is two problems with ultrasound being used to find images?
One problem with ultrasound is that they partially reflect when they meet a boundary between two densities. However, when scanning for a baby for example, a gel is used between the boundaries to minimise these reflections. Also, it cannot scan through bone.
Why is ultrasound better than x-rays?
Ultrasound does not cause mutations (unlike x-rays) and so does not have a risk of cancer.
What are seismic waves?
Seismic waves are produced by earthquakes, which are caused by sudden movements between plates in the earth’s crust. They carry the energy away from the earthquake.
What are P-waves?
P-waves are longitudinal and pass through both solids and liquids. They are faster than S-waves. They travel faster through solids than liquids.
What are S-waves?
S-waves are transverse and pass through only solids. They are slower than P-waves.
How did scientists know from earthquakes that the earth must contain a liquid core? (in terms of S-waves)
proof of liquid core of earth:
- S-waves can only travel through solids
- S-waves travel through the earth in curved paths due to changes in density throughout the mantle
- seisometers detect the waves once they pass through the earth
- there is an S-wave shadow zone where no waves can be detected, and this is there as the S-waves could not pass through the liquid core, which gave scientists evidence for a solid mantle and liquid core
How did scientists know from earthquakes that the earth must contain a liquid core? (in terms of P-waves)
proof of liquid core of earth:
- P-waves can travel through solids and liquids
- there are two parts of the earth where P-waves cannot be detected (P-wave shadow zones)
- they travel faster in solids than in liquids, so they slow down as they enter the liquid core, causing them to refract, and refract again when they leave the core
- this confirms the core is liquid
How did scientists know from earthquakes that the earth must contain a solid inner core?
proof of solid inner core of earth:
- sometimes, faint P-waves can be detected in the shadow zones, which was used by scientists to conclude that the earth has a solid inner core
What is echo sounding?
Echo sounding is using high frequency sound to detect objects in deep water and measure the depth.
What is an electromagnetic wave?
An electromagnetic wave is transverse and transfers energy from the source of the waves to the absorber. They do not need a medium to travel in.
Give the order of the visible light spectrum in terms of frequency and wavelength.
visible light spectrum:
- red (lowest frequency, highest wavelength)
- orange
- yellow
- green
- blue
- indigo
- violet (highest frequency, lowest wavelength)
Give the order of the electromagnetic spectrum.
the electromagnetic spectrum:
- radio waves (lowest frequency, highest wavelength)
- micro waves
- infrared
- visible light
- ultraviolet
- x rays
- gamma rays (highest frequency, lowest wavelength)
Why is the electromagnetic spectrum continuous?
The electromagnetic spectrum is continuous as the cut off point between each is not always clear.
What is the speed of all electromagnetic waves in a vacuum?
The speed of all electromagnetic waves in a vacuum is 300,000,000 m/s.
What three things can happen to an electromagnetic wave as it reaches a new material?
Materials absorb, transmit or reflect electromagnetic waves, but what happens depends on the wavelength and the difference in velocity.
How are waves depicted in wave front diagrams?
In wave front diagrams, the waves are a bunch of straight lines. (I I I I I) They connect all of the waves at the same point (eg. all of the troughs). When they slow down, they get closer together.
What happens when electromagnetic waves are generated or absorbed?
When electromagnetic waves are generated or absorbed, changes take place in atoms or in the nuclei of atoms. It causes changes to atoms (eg. electrons change energy levels).
Where are gamma rays emitted?
Gamma rays can be emitted from the nucleus of radioactive atoms.
What are the negative effects of ultraviolet waves?
Ultraviolet waves increase the risk of skin cancer and cause the skin to age prematurely. This is because it has hazardous effects on body tissue. The level of effects depend on the type of radiation and the size of the dose.
What are the negative effects of x-rays and gamma rays?
X-rays and gamma rays are ionising radiation, so they knock electrons off of the atoms, causing mutations. This is because it has hazardous effects on body tissue. The level of effects depend on the type of radiation and the size of the dose.
What is radiation dose a measure of?
Radiation dose is a measure of the risk of harm resulting from an exposure of the body to radiation. It is measured in sieverts (Sv).
Describe how radio waves are made and how they are received by radios to produce sound.
Radio waves can be produced when electrons oscillate in electrical circuits, which can then be absorbed (eg. by an aerial). The electrons in that circuit then oscillate in the same way, which creates an alternating current with the same frequency.
Give two uses of radio waves and why they are used for these purposes.
uses of radio waves:
- TV and radio
- they are used for this as they travel long distances before being absorbed
- they can reflect off of a layer of charged particles (the ionosphere) in the atmosphere, allowing them to travel very long distances
What is the ionosphere?
The ionosphere is a layer of charged particles in the atmosphere which can reflect radio waves, allowing them to stay in the atmosphere.
Give two uses of micro waves and why they are used for these purposes.
uses of micro waves:
- satellite communication, cooking
- used for this as most foods contain a lot of water molecules, and they absorb the energy from micro waves
- these waves can pass through the atmosphere without being reflected or refracted, so they are good for satellites in space
Give three uses of infrared and why they are used for these purposes.
uses of infrared:
- electrical heaters, cooking, infrared cameras
- used for this as the energy from infrared waves is easily absorbed by the surface of the object
Give one use of visible light and why they are used for this purpose.
use of visible light:
- fibre optic communications
- used for this as they have a short wavelength, so they can carry a great amount of information
Give two uses of ultraviolet and why they are used for these purposes.
uses of ultraviolet:
- energy efficient bulbs, sun tanning (can cause skin cancer)
- used for this as they have a short wavelength, so they carry more energy than visible light, and energy is absorbed by the internal surface of the bulb and is converted to visible light
Give one use of x-rays and gamma rays and why they are used for these purposes.
uses of x-rays and gamma rays:
- medical imaging and treatments
- used for this as they are very penetrative
- however, x-rays are absorbed by bones, so used in c-rays
What does a lens do?
A lens forms an image by refracting light.
What is the symbol for a convex lens?
convex lens:
What happens to the light rays in convex lenses?
In convex lenses, the light rays are bent towards the normal as they pass through the lens. If the ray is along the normal, nothing happens.
What is the principal axis?
The principal axis is the central ray which follows along the normal in lens diagrams.
What is the principal focus?
The principal focus is the point where all the rays focus. Its symbol is F.
What is the focal length?
The focal length is the distance from the centre of the lens to the principal focus. This depends on the strength of the lens.
Describe how to draw a ray diagram for a convex lens.
how to draw a ray diagram - convex lens:
- draw a line from top of object straight through the middle of the lens ((0,0) on the axis)
- draw a line from the top of the object parallel to the axis to where it meets the lens, and then connect this line going through F (given in exam)
- where lines meet is the image
- if lines don’t meet, draw dotted lines behind them until they meet; this is the image and it is virtual
What three things can an image be?
an image can be…
- diminished or magnified
- inverted or right way up
- real or virtual (real if meet at bold lines, virtual if dotted lines behind the object)
What is the symbol for a concave lens?
concave lens:
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What happens to the light waves in a concave lens?
In a concave lens, the light waves are diverged and bent away from the normal when they leave the lens. If the ray is along the normal, nothing happens.
Describe how to draw a ray diagram for a concave lens.
how to draw a ray diagram - concave lens:
- draw a line from the top of the object straight through the middle of the lens ((0,0) on the axis)
- draw a line from the top of the object parallel to the axis
- draw a dotted line connecting this line to the F before it and then continue in a bold line after the lens connected to this dotted line
- where the lines meet is the image
- if across a dotted line, the image is virtual
What is a magnifying glass, in terms of ray diagrams?
A magnifying glass is a convex lens where the object must be 1F or less. The image will be virtual.
What does each colour depend on?
Each colour has a narrow band of wavelength and frequency. The colour depends on which wavelengths are reflected, transmitted or absorbed.
How do coloured filters work?
Coloured filters work by absorbing certain wavelengths and transmitting other wavelengths.
What does it mean if objects are transparent?
Transparent objects transmit light and we can easily see through them due to specular reflection.
What does it mean if objects are translucent?
Translucent objects transmit light, but we can’t easily see through them due to diffuse reflection (they scatter the light rays).
What does it mean if objects are opaque?
Opaque objects are objects that we can’t see light through at all. The colour of the opaque object is determined by which wavelengths are more strongly reflected. (eg. white object has all light waves reflected, black object has all light waves absorbed)
Which electromagnetic wave do all objects emit and absorb?
All objects (bodies) emit and absorb infrared radiation. A hotter object will emit more infrared radiation.
Why do hotter objects produce visible light?
Both the wavelength and intensity of radiation depend on the temperature of an object. Hotter objects emit shorter wavelength radiation, so it will produce visible light. The intensity of radiation increases with temperature.
What is a perfect black body?
A perfect black body absorbs all of the radiation incident on it, so no radiation is transmitted or reflected.
Why is a perfect black body the best emitter of radiation?
A perfect black body is the best emitter of radiation as it completely absorbs, so it also completely emits.
How does temperature affect the absorption and emission of radiation?
If an object is a higher temperature than its surroundings, it will emit more radiation than it absorbs and for that reason, the temperature of it will drop. If the temperature is constant, the rate of emission and absorption is constant.
What radiation does the sun emit? What happens once this gets to earth?
The sun emits short wavelength radiation (visible light and ultraviolet) and this travels to earth. Some is reflected (eg. by clouds). The remaining waves are absorbed by the surface of the earth, so the temperature of the earth increases so the earth emits infrared back into space. Some is trapped as a greenhouse gas.
