WAVES Flashcards
What do waves do?
Transfer energy from one place to another without transferring any matter
What happens when waves travel through a medium?
The particles of the medium oscillate (vibrate) and transfer energy between each other
What is the amplitude of a wave?
The maximum displacement of a point on a wave from his undisturbed position
What is the wavelength of a wave?
The distance between the same point on two adjacent waves
What is the frequency of a wave?
The number of complete waves passing a certain point per second
What are transverse waves?
Vibrations go up and down (perpendicular to the direction of energy transfer)
What are examples of transverse waves?
All electromagnetic waves
Ripples and waves in water
What are examples of longitudinal waves?
Sound waves
Shock waves
What are longitudinal waves?
The vibrations are in the same direction the wave travels (side to side)
What is wave speed?
The speed at which energy is being transferred
What can happen when a wave arrives at a boundary?
Absorbed by material and energy is transferred to that energy store
The waves carry on travelling through the new material (refraction)
They are reflected
What is the angle of incidence?
The angle between the incoming wave and the normal
What is the angle of relfection?
The angle between the reflected wave and the normal
What is the angle of incidence equal to?
The angle of reflection
What is specular reflection?
When a wave is reflected in a single direction by a smooth surface
What is diffuse reflection?
When a wave is reflected by a rough surface
Why does diffuse reflection happen?
Because the normal is different for each incoming ray
What is the order of electromagnetic waves?
Radio waves
Micro waves
Infra red
Visible light
Ultra violet
X-rays
Gamma rays
What are electromagnetic waves?
Transverse waves that transfer energy from a source to an absorber
What is refraction?
When a wave crosses a boundary between materials at an angle and it changes direction
How does the speed of a wave affect its refraction?
If it slows down when it crosses the boundary it will bend towards the normal
If it speeds up as it crosses the boundary it will bend away from the normal
What is the optical density of an object?
The measure of how quickly light can travel through an object
What are radio waves used for?
Communication such as broadcasting TV and radio, communications and satellite transmissions
What do long radio wave signals do?
Bend around the earth because their long wave lengths diffract around the curved surface of the earth
What do long radio wave signals do?
Bend around the earth because their long wave lengths diffract around the curved surface of the earth (long distances)
What do short radio wave signals do?
Reflect off the ionosphere (long distances)
What are microwaves used for?
Communication to and from satellites
Microwave oven
What happens in microwave ovens?
The microwaves are absorbed by water molecules in the food (they transfer their energy to the molecules causing the water to heat up)
What is infrared radiation?
This is given out by all hot objects
What can infrared radiation be used for?
Electric heaters
Cooking food
What can visible light be used for?
Optical fibres in fibre optic cables which carry data over long distances as pulses of visible light (light rays bounce back and forth)
What can ultraviolet be used for?
Security pens
Produced by sun to give people tans
What can X-rays and gamma rays be used for?
X-ray photographs to see if any bones are broken
Treat cancer (kill cancer cells)
How does UV radiation cause harm to humans?
Damages surface cells
Blindness
Increased risk of skin cancer
How does gamma and x-rays cause harm to humans?
Ionising radiation so knock electrons off of atoms so can cause gene mutation or cell destruction and cancer
How do lenses form images?
By refracting light and changing its direction
What is the shape of a convex lens?
Bulges outwards
What is the shape of a concave lens?
Caves inwards
What is the axis of a lens?
A line passing through the middle
What is the principle focus of a lense?
Where rays coming out from the lens meet (or align back to for concave lenses)
What is the difference between a real and virtual image?
Virtual image is when both the image and the object are on the same side of the lens
How do you describe an image?
Magnified or smaller
Real or virtual
Upright or inverted
How do you draw a ray diagram for a convex lens?
From the top of the object draw:
a line going through the middle
a line parallel to axis then through the F
How do you draw a ray diagram for a concave lens?
From the top of the object draw:
a line going through the middle
a line parallel to axis then through the F the same side as the object
What images do concave lenses always make?
Virtual images
Upright
Smaller
What happens during refraction?
A wave meets a new medium (like glass) and slows down then returns to its normal speed out the other side
What do white objects do (light)?
Reflect all of the wavelengths of visible light
What do black objects do (light)?
Absorb all of the wavelengths of visible light
What are colour filters used for?
They are used to filter out different wave lengths of light so that only certain colours are transmitted and the rest are absorbed
What happens when white light is shone at a blue colour filter?
Only blue light will be let through and the rest will be absorbed
What would happen if a red hat was looked at through a blue filter?
The object would appear black as all of the light that is being reflected by the object will be absorbed by the filter
What are EM waves made of?
Made up of oscillating electric and magnetic fields
How are EM waves produced?
Alternating currents are made up of oscillating charges
As chargers ossification they produce oscillating electric and magnetic field
How can you make radio waves using an alternating current in an electrical circuit?
Transmitter charges oscillate to create radio waves
Energy carried by waves using AC in current reach a receiver and transferred to electrons
Energy causes electrons to oscillate and create AC
What are infrared cameras?
Detect infrared radiation and monitor temperature
How does infrared cameras work?
Detects IR radiation and turns it into electrical signal which can be displayed as picture on screen
What happens when an object absorbs infrared radiation?
It becomes hotter
How do electric heaters work?
Long piece of wire which has a current flowing through it which emits infrared radiation
Energy is transferred to objects thermal energy stores when they absorb the IR radiation
How do fluorescent lights work?
They absorb UV radiation and re emitt as visible light
What is a perfect black body?
An object that absorbs all of the radiation that hits it (no radiation reflected or transmitted)
What does the overall temp of the earth depend on?
The amount of radiation it reflects, absorbs and emits
What are sound waves caused by?
Vibrating objects
How do sound waves work?
Vibrating objects pass vibrations through surroundings medium as a series of compressions and rarefactions
Through what medium does sound usually travel fastest in?
Solids
Why can’t sound travel in space?
Because it is mostly a vacuum (no particles to move or vibrate)
How do your ears receive sound waves?
Causes ear drum to vibrate
Vibrations pass on to tiny bones called ossicles to the cochlea
Vibrations turned into electrical signals which get sent to brain
What is humans hearing sound range?
20Hz - 20kHz
What can sound waves be reflected by?
Hard flat surfaces
What can sound waves be reflected by?
Hard flat surfaces
What are echoes?
Reflected sound waves
Why do sound waves refract as they enter a different medium?
Enter denser material they speed up
Because wavelength changes but frequency remained the same so speeds up
What is ultrasound?
Sound with frequencies higher than 20000Hz
What is partial reflection of ultrasound?
Some passes from one medium to another and some of the wave is reflected off the boundary and some is transmitted
How can ultrasounds be useful?
Medical imaging
Industrial imaging
How can you use ultrasound to measure how far away a object is?
Point ultrasound at object
Some ultrasound gets reflected back at boundary
Time it takes for radiation to reach detector is how far away object is
What are the two types of seismic waves?
P and S waves
What are P waves?
Longitudinal
Travel through solids and liquids
Travel faster than S waves
What are S waves?
Transverse
Cant travel through liquids or gases
Slower than P waves
