P5 Flashcards
What are waves
An oscillation that transfers energy
What are longitudinal waves
Waves that have oscillations parallel to energy transfer
They require a medium like air as the energy is transferred when particles collide
When the oscillations are further apart there are rarefractions
When they are close together there are compressions
What are transverse waves
Waves that move (oscillate) at 90° to the direction of energy transfer
They do not always require a medium to travel through
What is amplitude
Distance from the trough to the crest of a wave (bottom to top)
Symbol - A
Measurement - depends on the wave, e.g m or v
What is wavelength
The distance from one point of a wave to the same point on the next eave
Symbol - λ - lambda
Unit - meters
What is frequency (waves)
The number of oscillations per second
Symbol - F
Units - Hertz
What is the time period (waves)
The time taken for a wave to pass a specific point
Symbol - T
Unit - seconds
What is wave velocity
The speed at which a wave transfers energy or information
How do you calculate wave velocity
Frequency × wavelength
How can waves be modeled
Using a ripples on water to model transverse waves
What happens when waves enter a different medium
Their velocity change causing the wave to refract
Why does entering a denser medium cause a wave to refract
Entering a denser medium causes the speed of the wave to decrease
So waves bend towards the normal
The wave length decreases and the frequency stays the same
What happens to sound waves at a boundary
They are either
Absorbed
Transmitted
Reflected
What is an echo
A refraction of sound
What is echo sounding
A process of finding the distance between two points, by using the time it takes to reflect a sound wave
What is sonar
Sound
Navigation
And
Ranging
It is used to find distances using echo-sounding
What is ultrasound
A sound frequency greater than 20,000hz
We cannot hear it but many animals can
Why is ultrasound usefull
It has a short wavelength so can easily be focused into a beam
How is ultrasound used
It can be used to make an image of a fetus
Ultrasound beams are transmitted into the mother (by the transmitter)
As there are different boundaries the waves are reflected and absorbed
The machine calculates the distance of each point using time and velocity, and those points are used to create an image
(Distance is divided by 2)
It is also used in sonar and echo-sounding
What happens when a sound wave hits a solid
After being reflected many times some of the sound is absorbed, making objects in the particle vibrate and heat up
How does your ear detect sound
The outer ear gathers the sound wave and directs it to the ear drum which vibrates
The ear drum makes the ossicles vibrate which amplify the vibration, passing it on to the inner ear.
The Cochlea then transmits these movements of the oval window to small hairs through a liquid.
These hairs (cillia) are attached to sound-detecting cells which release a chemical that causes a nerve to travel to the brain (auditory nerve)
Your brain then turns this into sounf
Why can we only hear certain frequencies
Hairs on your cochlea have a natural frequency
They have different lengths and resonate with different frequencies
The range of sound you can hear depends on the size of the hairs
The smaller the hairs the lower the frequency
Why do we stop being able to hear high frequency sounds as we get older
The short hairs that detect high frequencies fall out
What are electromagnetic waves
Transverse waves caused by oscillating electric and magnetic fields
They do not require matter - they all travel through a vacuum
What is a vacuum
A region with no particles of matter
What speed do electromagnetic waves travel at
3×10^8 m/s
This is the speed of light (which is in the electromagnetic spectrum)
What are the waves in the electromagnetic spectrum
Radio
Micro
Infrared
Visual light
Ultraviolet
X-rays
Gamma
What colours make up visible light
Red
Orange
Yellow
Green
Blue
Indigo
Violet
How does the wavelength and frequency change in the visible spectrum
Red light - lower frequency, longer wavelength
Violet - higher frequency. Shorter wavelength
Going from R→V The frequency increases and the wavelength decreases
How does the frequency and wavelength change in the electromagnetic spectrum
From Radio to Gamma
Wavelength decreases
Frequency increases
Why is infrared called what it is and why is ultraviolet called what it is
William Herschel split light and recorded the temperature of each frequency
Red was the hottest but he realised that there was an area past red called infrared
He found ultraviolet in the same way (it was colder)
How do we know EM waves can travel through a vacuum
The sun emits ultraviolet waves and space is a vacuum
What is the name of the object that electromagnetic waves transfer energy to
Absorbers
How are radio waves produced
An oscillating p.d across a wire causes electrons to move back and forth.
This produces a changing electric and magnetic field which releases radio waves
How are radio waves detected
When they meet an aerial (metal object), the electric field causes electrons to flow, so an electrical signal can move (and produce an image)
What electromagnetic waves are used in communication and examples
Microwaves - used in phones and communicating with satellite
Radio waves - sound and picture images are added to them to transmit television and radio signals
Infrared - remote controls use pulses of infrared to communicate with televisions
Visual light - used for ships to communicate
How are microwaves used in microwave ovens
Water and fat in the food absorb microwaves which heats up the outside of the food
Conduction transfers energy to the middle
What is conduction
Process of transferring heat between neighbouring particles
What are the dangers of EM waves
The waves with higher frequencies are the most damaging
Ultraviolet, x-rays and gamma rays can all damage your DNA causing mutations and cancer
UV rays damage DNA in skin cells
Gamma rays can even kill cells
What are the dangers of visible light, Infrared and microwaves
Visual light -Too much can cause blindness
Infrared - Can burn you
Microwaves - cause explosions (at a high enough frequency) in contact eith metals and internally heat cells
What are the dangers of radio waves
There are no known dangers
How are medical X-rays performed / what do they do
They were originally used to see bones and what is inside a person
Bones absorb X-rays while soft tissue like skin transmits it
Photographic film (placed behind the patient) darkens when in contact with x-rays, which can be used to see a persons internal structure
The white areas on photographic film are where the xrays have been absorbed by bones
How are medical X-rays performed / what do they do
They were originally used to see bones and what is inside a person
Bones absorb X-rays while soft tissue like skin transmits it
Photographic film darkens when in contact with x-rays, which can be used to see a persons internal structure
What does it mean if a wave is transmitted
It moves through the medium (refracted)
What does it mean if a wave is reflected
The waves bounce off the surface in a different direction - no energy is absorbed
What does it mean if a wave is absorbed
Energy is transferred from the wave to a medium
How are X-rays used in CT scans
There are different rates of absorption within the body
The points where x-rays are absorbed are used to create a 3D image
(Similar to ultrasound)
How are gamma rays used in medical imaging
It is used for imaging organs, e.g.the kidney
A patient is injected with radioactive tracers that emit gamma rays - that are transported to the target organ
By detecting the emitted gamma rays an image can be produced.
What is thermography
Taking images using a thermal imaging camera
What do thermal imaging cameras do
They detect infrared radiation which all objects constantly emit
The level of radiation detected depends on the temperature of the surface
Cooler surfaces are blue and hotter ones are red.
What is a thermogram and what is there medical use
An image that shows different temperatures
They are used to detect inflammation or infection, where the IR levels will be higher than expected
What are ray diagrams
Diagrams that show what happens when electromagnetic waves meet a boundary
How do you draw ray diagrams
Draw a normal 90° to the surface the wave is coming intact with
Draw the incident wave (the wave that hits the surface)
The draw the lines that show whether the wave has been reflected or refracted
The reflected wave will bounce off the surface at the same angle the incident wave hit it
What does it mean if something is resonant
It is oscillating at the same frequency as the object causing it to oscillate
What three things can happen to EM waves when they hit a surface
They are
Absorbed
Transmitted
Reflected
Why are radio waves reflected in the atmosphere
The earth is curved
To send radio waves over long distances they can be reflected in the ionosphere as they have a long enough wave length
How can microwaves be used to communicate with satellites
They can travel through the ionosphere as they have a high enough frequency
How do EM waves interact with walls (e.g house walls)
Walls transmit radio and microwaves, allowing your phones and tvs to work
They absorb visible light and ultraviolet
Which EM waves does the atmosphere absorb
X-rays and gamma rays
However some rocks emit gamma rays
What is a lens
A piece of transparent material that refracts light in a specific way.
Each lens refracts with a specific power
How do you find the power of a lens
1 ÷ focal length (m)
The power of a lens is measured in Dioptres
What are convex (converging lenses) and what are they used for
These lenses are thicker in the middle and reflect rays onto a principle focus, or focal point.
They are used to fix long sight, as they refract they light more, so close objects can be seen
What are concave (diverging lenses) and what are they used for
Lenses which are thinner in the middle and thicker on the outside
They refract parallel waves away from the focal point
Used to fix long sight as the light is normally refracted too much
What is the focal length
Distance between the centre of the lens and the focal point
What is a virtual image
An image produced (often by a mirror) that cannot be seen / projected on a screen
What is a real image
An image that can be projected on a screen
What determines whether an image will be real or visual in a convex lens
If the object is in front of the principle focus it will be a virtual image
If it is further away a real image can be formed
What is the principle axis
The line passing through the optical center
What is the optical centre
The centre of a lens
How can ray diagrams be used to predict where the image of the lens is
Draw a ray from the top of the object to the lens, parallel to the principal axis and from the lens to the focal point
Draw a ray from the top of the object, through the lens at the optical centre
Where the rays cross or appear to come from is where the image is
What types of images can convex lenses produce
Magnifying glass - virtual, magnified, upright
Camera / eye - real diminished inverted
What does it mean if an image is inverted
its upside down
The image is facing the opposite way to the object
What type of images do concave lenses produce
Spy holes in doors - virtual, diminished, upright
Back windows of coaches - virtual diminished upright
They are always virtual diminished and upright
How are rainbows formed
Light is made of different frequencies that travel at different speeds
Each frequency is refracted differently
Passing through a raindrop causes the light to refract as it has entered a denser medium - similar to a prism
This creates a rainbow
What is dispersion (light)
When white light is spread out into a spectrum
How do we see colour
The colour of an object is the colour that an object reflects
Grass appears green as it reflects all frequencies of light other than green
How do filters work (light)
A red filter absorbs all frequencies of light except red.
Red light can still be transmitted while the others cant
What is specular reflection
On a smooth surface, the reflected waves are all at the same angle as the incident rays
Specular reflection allows you to see images in paler
What is the law of reflection
The angle of incidence is equal to the angle of reflection
What is diffuse reflection
There is irregular scattering due to an uneven surface.
Each ray hits the surface at a different angle and is therefore reflected differently
Images can never be seen where there is diffuse reflection
