(Done) Waves (Paper 2) Flashcards
Describe the shape of a transverse wave
- The direction of oscillation is perpendicular to the direction of energy transferred by the wave
Describe the shape of a longitudinal wave
- The direction of oscillation is parallel to the direction of energy transferred by the wave
How do waves travel
- By transferring energy through a medium or a vacuum without transferring the particles in a medium
How do longitudinal waves travel
- The vibrations of particles in the medium are parallel to the direction the wave travels, transferring energy through compressions and rarefactions
What waves are transverse
- All electromagnetic waves e.g. light
- Waves in water
- Waves on a string
What waves are longitudinal
- Sound waves in air, ultrasound
- Shockwaves e.g. some seismic waves
What is the calculation relating wave speed, frequency and wave length
- Wave Speed = Frequency x Wave Length
What three things can happen when waves arrive at a boundary between two different materials
- The waves are absorbed by the material the wave is trying to cross into (Energy enters the materials energy stores
- The waves are transmitted often leading to refraction
- The waves are reflected
What rule should be followed for all reflected waves
- Angle of incidence = Angle of reflection
What is the normal in context of reflection
- An imaginary line perpendicular to the surface at the point of incidence
Define specular reflection
- When light is reflected in a single direction by a smooth surface e.g. a mirror
Define diffuse reflection
- When a wave is reflected by a rough surface and the reflected rays are scattered in lots of directions
Why does diffuse reflection occur
- The normal of each incoming ray is different due to the nature of a rough surface
What happens when diffuse reflection occurs
- The surface appears matte (not shiny) and you do not get a clear reflection of objects
Properties of all EM waves
- Transverse
- Travel at the same speed in air or a vacuum
List the waves within the EM spectrum
- Radio waves
- Micro waves
- Infrared waves
- Visible light
- Ultra violet
- X-rays
- Gamma rays
What is the wavelength of radio waves
- 1m - 10^4m
What is the wavelength of micro waves
- 10^-2m
What is the wavelength of infrared waves
- 10^-5m
What is the wavelength of visible light
- 10^-7m
What is the wavelength of ultra violet light
- 10^-8m
What is the wavelength of x-rays
- 10^-10m
What is the wavelength of gamma rays
- 10^-15m
What happens as the wavelength in the EM spectrum decreases
- Frequency increases
Why is there a large range of frequencies in EM waves
- EM waves are generated by a variety of changes in atoms and their nuclei
What determines where a wave is refracted
- The change in speed of the wave when it crosses into the second material
Define refraction
- When a wave crosses a boundary between materials at an angle and changes direction
What happens when a wave crosses a boundary and slows down
- It will bend towards the normal
What happens when a wave crosses a boundary and speeds up
- It will bend away from the normal
What changes occur when a wave is refracted
- The wavelength changes however the frequency stays the same
What happens when a wave is refracted whilst travelling along the normal
- The wave changes speed but is not refracted
Define optical density
- The measure of how quickly light can travel through it
What are EM waves made up of
- Oscillating electric and magnetic fields
What are alternating currents made up of
- Oscillating charges
What is the relation between alternating current and electromagnetic waves
- The oscillating charges within alternating current produce oscillating electric and magnetic fields producing EM waves
What factors of an alternating current will be given to the wave it produces
- Frequency
How are radio waves produced
- Using an alternating current in an electrical circuit
How are radio waves transmitted and received
- The object in which charges (electrons) oscillate to create the radio waves is called a transmitter
- When transmitted radio waves reach receiver, the radio waves are absorbed
- The energy carried by the waves is transferred to the electrons in the receiver
- This energy causes the electrons to oscillate and, if the receiver is part of a complete electrical circuit, it generates an alternating current
Define long-wave radio
- Waves with wavelengths between 1 and 10 km
How is long-wave radio transmitted around the world
- Long wavelengths diffract (bend) around the curved surface of the earth
- Long wavelengths can also diffract around hills and into tunnels
Define short-wave radio signals
- Radio waves with a wavelength of about 10m-100m
Define the ionosphere
- An electrically charged layer in the Earth’s upper atmosphere
How is short-wave radio transmitted around the world
- Short-wave radio is reflected from the ionosphere
Applications of short-wave radio
- Bluetooth
What conditions determine whether medium-wave signals can reflect off the ionosphere
- Atmospheric conditions
- Time of day
What are microwaves used for
- Microwave ovens
- Communication to and from satellites
Why are microwaves used to communicate with satellites
- They can pass easily through earth’s watery atmosphere
How do microwaves communicate with satelites
- Signal from a transmitter is transmitted into space
- Signal is picked up by the satellite receiver dish
- Satellite transmits the signal back to earth in a different location
- Signal is picked up by a satellite dish on the ground
How are microwaves used in microwave ovens
- Microwaves are absorbed by water molecules in the food
- Microwaves penetrate a few centimetres in the food being absorbed and transferring energy to the water molecules in the food causing the water to heat up
- The water molecules then transfer this energy to the rest of the molecules in the food by heating which quickly cooks the food
What is a use of infrared radiation
- To increase or monitor temperatures
How does infrared radiation occur
- Infrared radiation is given out by all hot objects - the hotter the object, the more radiation it gives out
How is infrared radiation used to monitor temperature
- Infrared cameras detect the radiation and turn it into an electrical signal which is displayed on a screen as a picture
- The hotter the object is, the brighter the image appears
How is infrared radiation used to increase temperature
- Absorbing infrared radiation causes objects to get hotter
What is a practical use of visible light
- Transmitting data via fibre optic cables
How is visible light used to transfer data via fibre optic cables
- Optical fibres can carry data over long distances vial pulses of visible light
- Light is reflected back and forth within the cables until they reach the end of the fibre
What is a use of ultraviolet light
- Fluorescent lights
How is ultraviolet light used for fluorescent lights
- Fluorescent chemicals emit visible light when ultra violet radiation is absorbed
- Fluorescent lights generate UV radiation, which is absorbed and re-emitted as visible light by a layer phosphor on the inside of the bulb
What are the practical uses of X-rays
- To take X-ray photographs
- To treat cancer
How are X-rays used to take X-ray photographs
- X-rays pass easily through soft tissue such as flesh however struggles to pass through denser material such as bone
- The plate of an X-ray begins white and becomes black, this is a negative image
- The white parts of the photo are where less X-rays got through therefore are the parts where X-rays where stopped by bones
How are X-rays and gamma rays used to treat cancer
- High doses of X-rays and gamma rays kill all living cells so are carefully directed to the cancer to treat it
What are the practical uses of gamma rays
- As a medical tracer
- To treat cancer
How are gamma rays used as medical tracers
- A gamma-emitting source is injected into a patient
- Its progress is followed around the body
- Gamma radiation is well suited for this because it can pass out of the body to be detected
What are the effects of each type of EM radiation based on
- How much energy the wave transfers
Damage caused by low frequency waves
- Don’t transfer much energy
- Mostly pass through soft tissue without being absorbed
Damage cause by high frequency waves
- Transfer lots of energy, possibly ionising
- Can cause gene mutation or cell destruction and cancer
Damage caused by UV radiation
- Damage surface cells
- Sunburn, skin ages prematurely
- Blindness, increased risk of skin cancer
What is radiation dose measured in
- Sieverts (Sv)
Name the two types of lens
- Concave
- Convex
Describe the shape of a concave and convex lens
- Concave bends inwards
- Convex bends outwards
What do concave and convex lenses do to light parallel to the axis
- Concave causes light to diverge from the principal focus
- Convex causes light to converge towards the principal focus
Define principal focus for concave and convex lenses
- For concave lenses, the principal focus is the point where rays hitting the lens parallel to the axis appear to all come from
- For convex lenses, the principal focus is where rays hitting the lens parallel to the axis all meet
Define focal length
- The distance from the centre of the lens to the principal focus
State the two rules for refraction in convex lenses
- An incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
- An incident ray passing through the principal focus refracts through the lens and travels parallel to the axis
State the two rules for refraction in concave lenses
- An incident ray parallel to the axis refracts through the lens and travels in line with the principal focus
- An incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis
Define a real image
- Where the light from an object comes together to form an image on a ‘screen’
Define virtual image
- When the rays are diverging so the light from an object appears to be coming from a completely different place
Three features which are needed to describe an image properly
- How big it is compared to the original object
- Whether it is upright or inverted
- Whether it is real or virtual
Features of an image produced from a concave lens
- Virtual image
- The right way up
- Smaller
- Same side of the lens as the object
What does colour and transparency of an object depend on
- Absorbed wavelengths
What causes objects to be opaque
- Light is not transmitted
- They absorb some light wavelengths and reflect the ones we see
What causes objects to be transparent or translucent
- Some or all light is transmitted through the object
Function of primary colour filters
- Only allows light of that colour to pass through the filter
- If that colour of light is not present, the object appears black
What properties are better than others at absorbing and emitting radiation
- Black is better that white
- Matt is better than shiny
Define a perfect black body
- An object that absorbs all the radiation that hits it
Properties of a perfect black body
- Best possible emitter of EM radiation
What is he overall temperature of the earth dependant on
- The amount of radiation it reflects, absorbs and emits
How do we hear sounds
- Sound waves that reach your ear drums can cause it to vibrate
- These vibrations are passed on through tiny bones in your ear called ossicles, through the semi-circular canals and to the cochlea
- The cochlea turns these vibrations into electrical signals which get sent to your brain which allow you to sense sound
State the human hearing range
- 20Hz - 20kHz
What factors limit the human hearing range
- Size and shape of the ear drum
- The structure of all the parts in the ear that vibrate to transfer energy from the sound wave
Define ultrasound
- Sound with frequencies higher than 20kHz
What is a practical use of Ultrasound
- Detecting how far away something is and developing an image from that
- E.g. medical imaging, industrial imaging
How is ultrasound used to find distance
- Ultrasound waves are partially reflected at wave boundaries
- Waves travel at fixed speeds in a medium
- The distance between the start point and the surface can be calculated by using the time taken for the ultrasound wave to return
Features of S waves
- Transverse
- Can only travel through solids
- Slower than P waves
Features of P waves
- Longitudinal
- Can travel through solids and liquids
