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