Waves Flashcards
What is a wave?
A vibration that transfers energy without transferring matter
What is a transverse wave?
A wave where the oscillations are perpendicular to the direction of energy transfer of the wave
What is a longitudinal wave?
A wave where the oscillations are parallel to the direction of energy transfer of the wave
What happens when waves travel through a medium?
The particles vibrate and transfer energy between each other but they stay in the same place
What are crests and troughs?
Points of maximum positive and maximum negative displacement from the particles rest position
What is the amplitude of a wave?
The maximum displacement of a point from its undisturbed position
What is the equation for the period of a wave?
Period= 1 over frequency.
What is the wavelength?
The distance between the same point on two adjacent waves.
What is the frequency?
The number of complete waves passing a certain point per second.
What is frequency measured in?
Hertz (Hz)
How can the speed of sound be measured using an oscilloscope?
Set up oscilloscope so the detected waves at each microphone as shown as separate waves, slowly move microphones away until two waves are aligned, measure distance between microphones to find wavelength then use formula
What can happen when waves arrive at a boundary between two different materials?
They can be absorbed by the material they are trying to pass into, they can be transmitted and keep on travelling (often leading to refraction) or they can be reflected
What is the rule for all reflected waves?
Angle of incidence = angle of reflection
What is the angle of incidence?
The angle between the incoming wave and the normal
What is the angle of reflection?
The angle between the reflected wave and the normal
What is the normal?
An imaginary line that’s perpendicular to the surface at the point of incidence, normally shown as a dotted line
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 and the reflected rays are scattered in lots of different directions
Why does diffuse reflection happen?
Because the normal is different for each incoming ray, which means that the angle of incidence is different for each ray
What are EM waves?
Waves that are transverse and transfer energy from a source to an absorber and all travel at the same speed through air or a vacuum
Give the EM spectrum, with each wave increasing frequency and decreasing wavelength
Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays
Why are there such a large range of frequencies in the EM spectrum?
Because EM waves are generated by a variety of changes in atoms and their nuclei
What is refraction?
When a wave crosses a boundary between materials at an angle and it changes direction
What does how much a wave refracts depend on?
How much the wave speeds up or slows down, which depends on the density of the two materials
How does speed affect a wave when crossing a boundary?
If it slows down it will bend towards the normal and if it speeds up it will bend away from the normal
How is wavelength and frequency affected when a wave is refracted?
Wavelength changes but frequency stays the same
What is the optical density of a material?
A measure of how quickly light can travel through it; the higher the optical density, the slower light waves travel through it
How do you construct a ray diagram for a refracted ray of light?
Draw a horizontal boundary, then draw the normal perpendicular to it, draw an incident ray that meets the normal at the boundary, then draw the refracted ray on the other side of the boundary.
How does the optical density affect the size of the angle of refraction in comparison to the size of the angle of incidence?
If the second material is optically denser than the first, the refracted ray bends towards the normal and the angle of refraction will be smaller than the angle of incidence
What are EM waves made up of?
Oscillating electric and magnetic fields
How are radio waves produced by an alternating current in an electrical circuit?
When transmitted radio waves reach a receiver, they are absorbed, the energy carried by the waves is transferred to the electron sin the material of the receiver, causing the electrons to oscillate, generating an alternating current which has the same frequency as the radio wave that generated
How long are the wavelegnths of radio waves?
Around 10 cm or longer
Why can long-wave radio be transmitted around the world?
The longer wavelengths diffract around the curved surface of the earth, as well as diffracting around things like hills or into tunnels
Why can short-wave radio signals be received at long distances away from the transmitter?
They are reflected from the ionosphere (an electrically charged layer in the earth’s upper atmosphere)
How does satellite TV work (in terms of waves)?
Microwaves are set from a transmitter on earth into space, where they are picked up by a satellite orbiting above earth. The satellite transmits the signal back to earth in a different direction whee it is received by a satellite dish on the ground
How do microwave ovens work?
The microwaves penetrate a few centimetres into the food before being absorbed and transferring the energy they are carrying to the water molecules in the food, causing the water to heat up, which cooks the rest of the food
What uses does infrared radiation have?
Infrared cameras (which detects the IR radiation and turns it into an electric signal) , cooking food as absorbing IR radiation causes an object to get hotter and electric heaters which emit IR radiation
How do fibre optic cables work?
Visible light rays are bounced back and forth until they reach the end of the fibre. The light is not easily absorbed or scattered as it travels along a fibre
Why do fluorescent colours look so bright?
Fluorescence is a property of certain chemicals, where UV radiation is absorbed and then visible light is emitted
What are the uses of UV radiation?
Fluorescent lights (same as colours except the visible light is radiated out by a layer as phosphorus), security pens which only show up under UV, suntans (from the sun) and UV lamps