6. Waves Flashcards
What type of wave is a sound wave?
Longitudinal
Which type of vibrations move parallel to the direction of the wave?
Longitudinal
Which type of vibrations move perpendicular to the direction of the wave?
Transverse
Which waves can’t travel through a vacuum?
Mechanical
Which waves can travel through a vacuum?
Electromagnetic
Which waves pass their vibrations through particles?
Mechanical
What is frequency measured in?
Hertz
If one wave passes per second, what is the frequency?
1 Hz
How do you work out frequency?
Frequency = 1 / Period
What is a period?
How long is takes for the wave to pass a point - messed in seconds
Equation for wave speed?
Wave speed = frequency x wavelength
Equation for frequency?
Frequency = speed / wavelength
Equation for wavelength?
Wavelength = speed / frequency
What is the symbol for wavelength?
Lambda
What does the angle of incidence equal?
The angle of reflection
When light enters a glass cube, which direction does it refract?
Towards the normal
What happens when light enters a denser glass block?
The speed of the wave decreases and it refracts towards the normal
When the incident ray leaves the glass block, which direction does it go in?
Away from the normal
What happens to the speed of the ray it leaves the glass block?
It speeds up and bends away from the normal
What is the speed of a wave through a vacuum?
300,000,000 or 3x10 to the power of 8
Do different electromagnetic waves carry different amount of energy?
Yes
What happens when a ray is absorbed instead of reflected?
It heats up
What happens as the energy of a wave increases?
The temperature and hazard increased
What happens as the wavelength decreases?
The frequency increases The energy carried increases The waves become more dangerous The waves diffract less The waves have a shorter range The waves carry more information
What are the groups in the electromagnetic spectrum?
Gamma X-ray Ultraviolet Visible Infrared Microwaves Radio waves
What type of electromagnetic wave has the highest frequency and energy, and the shortest wavelength?
Gamma
What type of electromagnetic wave has the lowest frequency and energy, and the longest wavelength?
Radio waves
What are infrared waves used for?
To locate fire, detect humans and night vision
What type of wave is a light wave?
Transverse
What are radio waves used for?
Radio, TV, telecommunications
What are gamma waves used for?
Kills bacteria, radiotherapy, cancer treatment
What are microwaves used for?
Radar detection, satellite communications, cooking
What are in X-rays used for?
Examine damaged machinery and medical scans
What are visible waves used for?
Computers, TV, LED display, to see
What are ultraviolet waves used for?
Detect counterfeit banknotes
What are the hazards of infrared waves?
Overheating - burning
What are the hazards of radio waves?
None
What are the hazards of gamma waves?
Cancer mutations to tissue
What are the hazards of microwaves?
Damage parts of brain
What are the hazards of X-Ray’s?
Body cells can be killed by high doses
What are the hazards of visible waves?
Intense beam damages eyes
What are the hazards of ultraviolet waves?
Sun burn, skin cancer
How are sounds made?
When an object vibrates and it causes the layer of air next to it to vibrate
Where do sounds travel fastest? Why?
Solids because the particles are closer together
Why is the no sound in a vacuum?
Because there are no particles to vibrate and pass on energy
What do you need to remember when doing f=v/lambda
MAKE SURE THAT THE WAVELENGTH IS IN METRES, THE TIME IN SECONDS AND FREQUENCY IN HZ
What is the range of normal human hearing?
20Hz to 20,000Hz
When will sound waves refract?
When air changes temperature (change in medium) - waves will travel slower in cooler air
Where does sound refract in the night?
Downwards, the air near the ground is cooler than the air higher up
What frequency are ultrasound waves?
Higher than 20,000Hz
When are ultrasound waves reflected?
When they reach a boundary between two different media
How do you determine how far away a boundary is?
How long the reflections take to reach the detector
What is ultrasound used for?
Medical
Industrial cleaning and no destructive testing of materials
Why does the ultrasound need to be a pulse?
So you can hear the echo
How is the time delay for an ultrasound and pulse worked out?
distance = speed x time
Why is gel used in ultrasound?
Because then there is more ultrasound absorbed. When there is a big difference between densities lots of it would be reflected.
What is the distance in ultrasound?
The way there and back
What is the depth in ultrasound?
Just the way there
Other uses of ultrasound?
The detection and removal of kidney stones
What makes seismic waves?
A sudden release of energy in the earths crust
What is used to detect movements of the earths crust?
A seismometer
What are the two types of seismic wave?
Primary and secondary
Properties of primary waves?
- longitudinal
- travels through solids and liquids
- travels faster
Properties of secondary waves?
- transverse
- only travel through solids
- travels slower
How does heat travel through space?
By infrared waves
What emits and absorbs thermal radiation?
All bodies
What is thermal (infrared) radiation?
The transfer of energy by electromagnetic waves
What is a thermograph?
The images taken using infrared radiation
What surface is the best emitter of infrared radiation?
Matte black surfaces
What surface is the worst emitter of infrared radiation?
Silver (shiny) surfaces
Best materials to emit infrared radiation? Best to worst
Matte black, shiny black, white, silver
Which kettle will cool down faster: black or metallic?
Black because it will emit more radiation
What direction does heat energy flow in?
From a hot object to a cooler one
What do good emitters also act as?
Good absorbers
What surface is the best absorber of infrared radiation?
Matte black surfaces
What surface is the worst absorber of infrared radiation?
Silver surfaces
Best materials to absorb infrared radiation? Best to worst
Matte black, shiny black, white, silver
Why are shiny surfaces the worst absorbers?
They reflect most of the radiation away
Why do solar panels have a black outer layer?
So it can absorb heat
Why are firefighters suits shiny?
They are the worst absorbers, the the best reflectors
Why is the back of a solar panel silver?
Reflect heat back onto pipes
Why are premature babies wrapped in silver blankets?
Its the worst emitter, so reduces the amount of heat that they lose
Why are radiators in car engines black?
It’s the best emitter
What is a perfect black body?
An object that absorbs all the radiation that hits it
What does a perfect black body not do?
Reflect or transmit any radiation
What is the radiation emitted by a black body called?
Black body radiation
What is black body radiation?
The radiation emitted by a black body
If an object’s temperature is higher, what will happen to the infrared radiation it’s emitting?
Higher temperature -> more infrared radiation emitted in a given time
What happens as a filament lamp warms up?
- doesn’t glow, emits infrared
- warms up glows dull red -> emitting visible spectrum
- orange-red
- yellow-white as filament gets hotter
What does the intensity of radiation at a certain wavelength depend on?
Temperature
What happens as temperature and radiation increases?
Radiation increases at every wavelength and the peak moves to a shorter wavelength (high frequency)
What happens to radiation as temperature increases?
If temperature increases, intensity of radiation increases at every wavelength so peak moves to a shorter wavelength
What does the temperature of the earth depend on?
- The rate that light and infrared radiation are absorbed by the atmosphere/surface or are reflected back into space
- The rate at which the earth emits radiation from its surface and atmosphere
Where does the sun’s spectrum peak?
At visible wavelengths
What are the two major types of lens?
- concave
* convex
What can concave lenses also be known as?
Diverging lenses
What can convex lenses also be known as?
Converging lenses
When is there a principal focus?
When the light rays are parallel
In a convex lens, how does the thickness of the lens affect the focal length?
The thicker the lens, the shorter the focal length
What is the shape of a converging lens?
It is thicker at the centre than the edges
What is the shape of a diverging lens?
It is thinner at the centre than the edges
How is magnification calculated?
magnification = image height / object height
If the image is larger than the object what is the magnification equal to?
greater than 1
If the image is smaller than the object what is the magnification equal to?
less than 1
What can the image in a convex lens be?
- real or virtual
- magnified or diminished
- upright or inverted
How is the image transformed in a camera?
(convex lens)
- diminished
- inverted
- real
How is the image transformed in a projector?
(convex lens)
- magnified
- inverted
- real
How is the image transformed in a magnifying glass?
(convex lens)
- magnified
- upright
- virtual
What type of images do convex lenses give?
- virtual
- upright
- diminished
What happens in a convex lens when the object moves further away from the lens?
The image gets smaller and moves away from the lens
How is short-sightedness corrected?
The eyeball is elongated so needs a concave lens
How is long-sightedness corrected?
Convex lens
Why does white light spread out into colours after it passes through a glass pyramid?
The different wavelengths experiences different changes in speed as they enter and leave the glass so refract by different amounts
Which colours are refracted the most and the least?
- red is refracted the least
* violet is refracted the most
What are the primary colours of light?
Red, green, blue
What are the secondary colours of light?
Yellow, cyan, magenta
What does green and blue light create?
Cyan light
What does green and red light create?
Yellow light
What does green and red light create?
Magenta light
What does a filter do?
Only allows a small range of wavelengths to pass through
What does a red filter do?
Only allows red light through and absorbs blue and green light
What are opaque objects?
Those that do not transmit light
What does the colour that an objects appears depend on?
Which wavelengths are most strongly reflected
Why do objects appear white?
They reflect all of the wavelengths of visible light equally
Why does a red object look black through a blue filter?
A red object only reflects red light and the blue filter only transmits blue light, so only blue light shines on the red object and it is absorbed so it appears black
How is a light ray reflected by flat foil?
Reflected in a single direction (specular reflection)
How is a light ray reflected by crumpled foil?
Scattered (diffuse reflection)
