Flashcards in Section 2 - Waves and the Electromagnetic Spectrum Deck (82):
What do waves do?
They transfer information and energy without transferring matter.
What is amplitude?
Half the displacement from crest to trough.
What is wavelength?
The length of a full wave cycle.
What is frequency?
The number of cycles per second.
What is frequency measured in?
Hertz (Hz), 1Hz = 1 wave per second.
What is a period?
The number of seconds per cycle.
Describe the equation linking wave period and frequency.
Period= 1/ frequency
In transverse waves, which direction do the particles oscillate?
Perpendicular to the direction of energy transfer.
In longitudinal waves, which direction do the particles oscillate?
Parallel to the direction of energy transfer.
What piece of equipment is used to visualise waves?
What are the equations for wave speed?
V = wave speed
x = distance
t = time
f = frequency
λ = wavelength
What is wave speed?
How quickly a wave moves through a medium.
What is a boundary?
An interface between mediums.
What can happen to waves crossing boundaries?
They can be absorbed, reflected or transmitted, which can lead to refraction.
What is absorption?
The wave's energy is transferred to the material's energy store.
What is transmission?
Where the wave is allowed to travel through a material.
What is reflection?
The incoming wave is neither absorbed or transmitted and is instead bounces back away from the material.
What is refraction?
A change in direction during transmission.
How does refraction occur?
Waves travel at different speeds in different mediums depending on density. If a wave crosses a boundary at an angle, this change in speed causes a change in direction.
If a wave slows down in transmission over a boundary, what direction does the wave bend?
Towards the normal.
If a wave speeds up in transmission over a boundary, what direction does the wave bend?
Away from the normal.
What trend do most em waves follow in with wave speed and medium density?
They move slower in denser mediums.
How does the size of the change in speed affect the angle of refraction?
The larger the change in speed, the larger the refraction.
What happens if a wave is transmitted along the normal?
It will not be refracted, instead it will continue to travel in the same direction.
What happens to the frequency when a wave crosses a boundary?
It remains the same.
What happens to wavelength when a wavelength crosses a boundary?
It changes, elongating or shortening depending on the change in density between the two mediums.
What diagrams are used to draw the refraction of waves?
Ray diagrams and wave front diagrams.
What do ray diagrams show?
The effects of boundaries on a light ray.
What do wave front diagrams show?
The effects of boundaries on any ray.
What causes sound waves?
What type of wave is a sound wave?
How do longitudinal waves travel?
As a series of compressions and rarefactions.
What trend do most sound waves follow with wave speed and medium density?
The denser the medium is, the higher the wave speed.
How are sound waves affected by hard, flat surfaces?
It will reflect, causing echoes.
What are the different parts of the ear?
The outer ear, the eardrum, the ossicles, the semicircular canals, the cochlea and the auditory nerve.
How does the ear function?
Sound waves reach the eardrum, causing it to vibrate.
These vibrations are passed onto the ossicles, tiny bones in the ear.
The ossicles pass the vibration through the semicircular canals to the cochlea.
The cochlea turns the vibrations into electrical signals and passes it through the auditory nerve to the brain,
The brain interprets these signals as different volumes and pitches, higher frequency leads to higher pitch and higher intensity means louder volume.
What are the three ossicles called?
Hammer, anvil and stirrup.
What is the human hearing range?
What is ultrasound?
Sounds above 20000Hz
What happens to ultrasound at boundaries?
It is partially reflected.
What are some uses of ultrasound?
Medical imaging like a pre-natal scanning of a foetus, industrial imaging, to find flaws in materials and sonar.
What is infrasound?
Sound bellow 20Hz
What are some uses of infrasound?
Animal tracking and earthquake prediction.
What are seismic waves caused by?
Earthquakes and explosions.
What are seismic waves?
Waves that travel through the earth.
What are the two main types of seismic wave?
P-waves ans S-waves.
What are the properties of P-waves?
They are longitudinal and travel through both solids and liquids, they are also the faster of the main two seismic waves.
What are the properties of S-waves
They are transverse and can only travel through solids, they are also the slower of the two seismic waves.
What are the layers of the earth? What states are they?
The crust (solid), the mantle (almost solid), the outer core (liquid) and the inner core (liquid).
Describe the equation relating angle of incidence and angle of reflection.
Angle of incidence = angle of reflection.
What is total internal reflection?
A wave hitting a surface is reflected back into the material.
How does total internal reflection occur?
The wave must be traveling through a dense material to a less dense one with an angle of incidence larger than that material's critical angle.
What are the two types of reflection?
Specular and diffuse.
What is specular reflection? What is the reflection like?
When light is reflected by a smooth surface, leading to reflection in a single direction, this leads to a clear reflection.
What is diffuse reflection? What is the reflection like?
When light is reflected by a rough surface, leading to reflection in all directions, this leads to a matt reflection- or no clear reflection.
How does light form different colours?
The different wavelengths affect our eyes differently.
If an object appears to be black, what is happening to the light?
It is being absorbed so no light is reflected or transmitted.
If an object appears to be white, what is happening to the light?
It is being reflected so no light is being absorbed or transmitted.
If an object appears to be see through, what is happening to the light? What is this called?
It is being transmitted, this makes the object either transparent or translucent.
If an object appears to not be see through, what is happening to the light? What is this called?
It is being absorbed or reflected, this makes the object opaque.
What are the two main types of lens?
Converging and diverging.
What is a converging lens?
A lens that bulges out in the middle and causes parallel rays of light to be brought closer together at the focus.
What is a diverging lens?
A lens that caves in at the middle and causes parallel rays of light to be spread out.
What is a real image? How is it formed?
An image that can be captured on a screen, it is formed when light rays come together to form the image, it can be captured because the rays actually meet where the image appears to be. It is formed by a converging lens.
What is a virtual image? How is it formed?
An image where the light rays appear to be coming from a completely different place than where they are actually coming from, it can't be captured on a screen because the light rays aren't actually meeting, it is caused by a diverging lens.
How does curvature affect the power of a lens?
The power of a lens increases with it's curvature.
List the EM spectrum.
List the visible light spectrum.
How does peak wavelength change as things get hotter?
How does intensity change as things get hotter?
What is intensity?
Power per unit area.
How is intensity related to wavelength?
Intensity increases more rapidly in shorter wavelengths.
How is EM emission effected by colour?
Dull black materials are better emitters than shiny white ones.
How are EM waves produced?
By oscillating charges.
What are radio waves used for?
Communication and broadcasting.
How can long-wave radio travel large distances?
Its large wavelength allows it to be bent around the earth's curvature.
How can short-wave radio travel large distances?
Its shorter wavelength allows it to be reflected by the earths atmosphere.
Why doesn't TV or FM radio travel very far?
The signal doesn't bend or travel through buildings.
What waves do satellites use? Why?
Micro waves and high frequency radio waves, because they can penetrate the earth's watery atmosphere.
In microwave ovens, how is EM radiation employed?
The wavelength is different to communication micro waves and can be absorbed by water, this allows the wave to penetrate a few centimeters into the food before transferring its energy into the water molecules in the food, causing it to heat up.
How is infra red radiation used?
Thermal imaging, increase temperature or transfer information in remote controls or fibre optics.