Waves Flashcards
What is the amplitude of a wave?
Maximum displacement of a point on a wave from its undisturbed position
What is a wavelength?
The distance between the same point on two adjacent waves
What is frequency?
The number of complete waves passing through a certain point per second
Equation for time period
Period = 1/frequency
What are transverse waves & 2 examples
Oscillations are perpendicular to the direction of energy transfer (electromagnetic waves (light))
What are longitudinal waves
Oscillations are parallel to direction of energy transfer (sound)
Equation for wavespeed
Speed = frequency x wavelength
What are 3 things that can happen when waves arrive at a boundary between two materials?
- Waves are absorbed and their energy is transferred into the material’s energy stores
- Waves are transmitted and carry on travelling through the material (refraction)
- Waves are reflected
What does angle of reflection equal?
Angle of incidence to the normal
What is specular reflection?
When a wave is reflected in a single direction off a smooth surface
What is diffuse reflection?
When reflected waves are scattered in random directions off a bumpy surface
Why can diffuse reflections not be seen?
Each ray has a different normal, so all angle of reflections are different because angle of incidence = angle of reflection
What do all EM waves do?
Travel at the speed of light through air
State the EM spectrum in order of lowest to highest frequency
- Radio waves
- Microwaves
- Infra red
- Visible light
- Ultra violet
- X rays
- Gamma rays
What is refraction?
When a wave enters a different material at a different angle to the normal, so changes direction
What affects the amount of refraction?
How much the waves speeds up/ slows down, which depends on the density of materials (higher the density, the slower the wave travels through it)
What is optical density?
How quickly light can travel through a material (higher density, slower light)
Refraction ray diagram for an optically denser material?
The angle of refraction will be smaller than the angle of incidence - bends towards the boundary
Refraction ray diagram for a less optically dense material?
The angle of refraction will be bigger than the angle of incidence - bends away from the boundary
How do electromagnetic waves form?
Alternating currents are made up of oscillating charges which produce oscillating magnetic and electric fields
What is the frequency of an electromagnetic wave determined by?
The frequency of the alternating current it is formed from
How are radio waves produced?
- A transmitter charges electrons to oscillate
- When transmitted waves reach a receiver, the waves are absorbed
- Energy deposited by the wave transfers to the electrons
- If the receiver is part of an electrical circuit, an AC is produced
How do long wavelengths travel to a receiver which is not in line of sight?
They can diffract around obstacles like hills and tunnels
How do short wave radio signals travel long distance?
They reflect off of the ionosphere in the Earth’s atmosphere
DUHS of radio waves
D = antennae or aerial
U = Radio communication
H = Negligible
S= antennae or aerial
DUHS of microwaves
D = antennae or aerial
U = mobile phones
H = over heating
S = magnetron
How do microwaves get from a transmitter to a mobile phone?
The wave is directed into space and reflects off of the satellite in space to a phone
Why are different wavelengths of microwave used in ovens and phones?
Communication microwaves need to travel through Earth’s watery atmosphere, whereas in ovens they need to be absorbed by water molecules in the food
How do microwaves quickly cook food?
Penetrate the food and get absorbed by water molecules, transferring their energy to the food , causing the water to heat up, cooking the food
DUHS for infrared radiation
D = infrared cameras
U = remote controls
H = burns
S = Sun
DUHS for visible light
D = eyes
U = to see
H = laser damage
S = lamps
DUHS for ultra violet
D = fluorescence glowing
U = tanning
H = skin damage
S = UV lamps
DUHS for x rays
D = photographic film
U = imaging broken bones
H = cancer
S = electron transmission
DUHS for gamma rays
D = Geiger Muller tube
U = radiotherapy
H = cancer
S = gamma ray bursts
How do optical fibres carry data?
Visible light rays reflect back and forth off the sides of the cable as they are glass
How do fluorescent lights work?
They emit UV light which is absorbed and re emitted as visible light by a layer of phosphorous
Why are higher frequency waves more dangerous?
They transfer lots of energy
Why are gamma and x rays most dangerous?
They are ionizing rays which can cause gene mutation or cell destruction
How is a radiation dose measured?
Sieverts
What do convex lenses do to light?
They cause light to converge at the focal point
What do concave lenses do to light?
They cause light to diverge
What is the principal focus for a convex lense?
Where all the rays of light meet in front of the lens
What is the principal focus for a concave lens?
Where all the rays come from on the axis behind the lens
3 rules for refraction in a convex lens?
- An incident ray parallel to the axis refracts through the lens and passes through the principal focus
- An incident ray travelling the opposite way travels through the principal focus and refracts through the lens to travel parallel
- An incident ray travelling through the centre of a lens keeps going the same direction
3 rules for refraction in a concave lens?
- An incident ray travelling parallel to the axis refracts to travel in line with the principal focus so it appears to come from the principal focus
- An incident ray traveling the opposite way in line with the principal focus refracts through the lens to travel parallel
- An incident ray passing through the centre of the lens carries on
What is a “real” image
When light comes together to form an image on a screen
What is a virtual image
When rays diverge, so the image seems to be in a completely different place
3 descriptors for an image?
- Size
- Upright or inverted
- Real or virtual
How to draw a ray diagram for a convex lens?
- From the top of the object, draw a line parallel to the axis
- Draw another ray going through the middle of the lens from the top of the object
- Refract the first ray through the focal point
- The mid lens ray does not change
- Where the rays meet is the top of the object
What will an object at 2x the focal point exactly create?
- Same size
- Inverted
- Real
What will an object between F and 2F create?
- Bigger
- Inverted
- Real
What will an object nearer to F create?
- Bigger
- Right way up
- virtual
How to draw a ray diagram for a concave lens?
- Draw a ray from the top of the object parallel to the axis
- Draw another ray from the object to the middle of the lens
- Refract the first ray, so that it appears as if it is coming from the focal point
- The ray passing through the centre doesn’t change
- Where the rays meet is the image
What do concave lens images always have?
- Smaller
- Right way up
- Virtual
Useful phrase for virtual images?
You can’t project virtual images onto a screen
What is the range of wavelengths for visible light?
400nm to 700nm
How do opaque objects receive light?
- They do not transmit
- Absorb some and reflect some
How is the colour of an opaque object determined?
Which wavelengths of light are most strongly reflected
Two possibilities for secondary colour objects?
- Reflecting that wavelength of visible light (yellow)
- Reflecting both primary colours (green and red light)
What do white objects do?
Reflect all wavelengths of light equally
What do black objects do?
Absorb all wavelengths
What do transparent objects do with light?
Transmit light, let some pass through
What do colour filters do?
Filter out certain wavelengths, so only some are transmitted and the rest are absorbed
How do primary colour filters work?
Only transmit their colour light and absorb everything else
What would happen to a red object when viewed through a blue filter?
It would appear black as all other wavelengths of light that are not blue are absorbed
What do secondary colour filters do?
Transmit wavelengths of their colour AND the primary colours used to make that colour (a yellow filter transmits green, red and yellow)
How do objects surroundings hotter than their cool down?
They emit more infrared radiation than they absorb
What surface is best at emitting/ absorbing radiation?
Black, matte
What surface is worst at emitting/ absorbing radiation?
White, shiny
What is a black body?
A perfect black body absorbs all radiation that hits it - nothing is reflected or transmitted
3 ways distribution of intensity changes as temperature increases?
- Intensity of all wavelengths increase
- Peak intensity occurs at a shorter wavelength
- Shorter the wavelength, quicker the increase in intensity
Why is nighttime colder than daytime?
In the day, lots of radiation is transferred to the earth from the Sun and absorbed, whereas at night time less radiation is being absorbed than is being emitted
How do sound waves transfer information?
By making particles vibrate creating a series of compressions and rarefactions
How do we hear?
- Soundwaves make the ear drum vibrate
- These vibrations are passed onto tiny bones called ossicles
- The cochlea turns these vibrations into electrical signals sent to the brain
What is the human hearing range?
20 Hz to 20 000 Hz
What is ultrasound?
A sound with a frequency higher than 20 000 Hz
What happens to ultrasound at boundaries?
They are partially reflected and some are refracted
3 uses of ultrasound?
- Medical screening e.g a foetus in the womb, as when ultrasound meets a boundary some is reflected back, meaning the exact time and distribution of these echoes can produce a video image
- Industrial screening
- Submarines to detect depth of water
How are seismic waves used to determine the location of an earthquake?
Time taken for waves to reach a seismometer
Properties of P waves?
- Longitudinal
- Travel through solids and liquids
- Faster than S waves
Properties of S waves?
- Transverse
- Only travel through solids
- Slower than P waves
