P6 Flashcards
Name the 2 categories of waves and give examples of each
- transverse wave = waves on water, electromagnetic spectrum (radio waves, microwaves, infra red, visible light, UV, x-rays, gamma rays)
- longitudinal wave = sound waves and ultrasound (and infrasound)
Describe the movement of particles in a transverse
the direction of particle oscillation (movement) is at right angles (perpendicular) to the direction of travel of the wave
Describe the movement of particles in a longitudinal wave
the direction of particle oscillation (movement) is backwards and forwards in a direction that is parallel to the direction of travel of the wave
Waves transfer energy, but not matter. Describe evidence for this statement
BUOY : (water)
- when the wave passes the buoy, it moves up and down as the wave moves the particles in the water up and down.
- however, the buoy does not get carried along in the direction the wave is travelling
EAR : (air)
- when the sound wave hits the eardrum, the eardrum vibrates backwards and forwards as the particles oscillate
- the wave does NOT push air into the ear, or the eardrum could burst
Compare longitudinal and transverse waves
- in a transverse wave, the particles oscillate at right angles to the direction of travel of the wave
- however, in a longitudinal wave, the particles oscillate backwards and forwards in a direction parallel to the direction of travel of the wave
- one similarity between both types of wave is that they both transfer energy but do not transfer matter
What is the definition of an amplitude?
- of a wave is the maximum displacement of a point on a wave away from its undisturbed position
What is the definition of a wavelength?
- of a wave is the distance from a point on one wave to the equivalent point on the adjacent wave
What is the definition of a frequency?
- of a wave is the number of waves passing a point each second
What is the definition of a period?
- this is the time taken for one wave to pass a point
What is the equation for calculating period?
period = 1/ frequency
```
T = 1/f
s) = 1/ (Hz
~~~
What is the equation for calculating wave speed?
wave speed = frequency x wavelength
```
v = fλ
m/s) = (Hz) x (m
~~~
Write a method to calculate the speed of sound
- standing about 500m away from a wall, Student A should hit the wood pieces together at the same time as student B presses ‘start’ on a stopwatch
- student B then stops the stopwatch when he hears the echo which has reflected off the wall
- then measure the exact distance between where student A is standing and the wall, using a tape measure and multiply this distance by 2 (as the sound travelled there and back again in the time
- now divide the distance the sound covered, by the time recorded to calculate the speed of the sound (speed = distance/time)
Write a method to calculate the speed of ripples on water
- set up a slow motion camera to film a shallow tray of water and press record - using the camera will ensure results are as accurate as possible, as time can be measured accurately
- drop a small pebble into the water (make a mark on the bottom of the tray and aim for the pebble to fall exactly over the mark)
- check the footage and determine the time it took for the ripple caused by the pebble to reach the edge of the tray - measure this distance with a ruler)
- now use the equation speed = distance/time to calculate the speed of the wave
What 3 things can happen when waves hit a substance?
- Absorbed - eg: food absorbs microwaves in a microwave oven
- Transmitted - eg: lenses in glasses and cameras allow light to pass through. sometimes the wave bends as it is transmitted - this is called refraction
- Reflected - eg. echoes
What is the boundary?
- a reflective surface (eg: mirror)
What is the incident ray?
- the ray that is going towards the boundary
What is the normal?
- a line drawn at 90o to the boundary at the point where the incidence ray hits the boundary
What is the reflected ray?
- the ray that is reflected away from the boundary
What is the Law of Reflection?
the angle of incident is equal to the angle of reflection
When a straw is in a glass of water ,the straw appears to be bending. What is this effect called?
- refraction
Why does the light appear to bed?
- when a wave crosses a boundary between 2 material it changes speed
What does the speed of the wave depend on?
- how much a wave speeds up or slows down depends on the (optimum) density of the 2 material
Explain what would happen to the speed of the light if it passed from the air into a clear plastic black
the light will slow down as it is entering a more denser than air
What would be the effect of this change of speed?
- the light slows down because it will bend (refract) towards the normal
What would happen to the speed and the direction of the light ray as it left that block?
- as the ight leaves the block it will speed up because the density decrease
- then it will refract (bend) away from the normal
What useful way do we have to remember what happens to the rays when they meet a boundary between different materials?
F . A . S . T
fast, away, slow, toward
The diagrams shows two beakers. Both beakers have a drawing pin inside as shown
The first beaker is empty. The eye cannot see the drawing pin. The second beaker is full of water and the eye can see the drawing pin
Explain how the eye is able so see the drawing pin in the second beaker
- the ray (drawn straight) to water surface refracts/bends away from the normal
- the refracted ray (drawn straight) enters the eye
What is a wave front?
- is basically the crest of a wave when viewed from above
What will happen to the wavelength of a wave if the wave speed decrease?
- wavelength will be smaller
What is the key point wavelength?
- if a wave slows down, it’s wavelength will decrease
- if a wave speeds up, its wavelength will increase
EXAMPLE 1:
If a wave passes from a less dense material into a more dense material it will…..
This means the wavelength will…
On the diagram, the wave fronts should be drawn
- slow done
- decrease
- closer together
EXAMPLE 2:
If a wave passes from a more dense material into a less material it will….
This means the wavelength will….
On the diagram, the wave fronts should be drawn….
- speed up
- increase
- further apart
What useful way do we have to remember the electromagnetic spectrum (from long-short wavelength) ?
Rotten Men Inevitably Visit Ugly X Girlfriend
Radio wave Microwaves Infrared Visible light Ultraviolet X-rays Gamma rays
Describe an example that shows how energy is transferred by EM waves
- a campfire is a source. It transfers energy to its surroundings by giving out infrared radiation, which is a type of electromagnetic wave
- these infrared waves are absorbed by objects
- energy is transferred to the object’s thermal energy stores
- this causes the object’s temperature to increase
How are radio waves produced and then used to produce a signal in the circuit of a car stereo?
- when an alternating current flows in a transmitter, electrons oscillate (vibrate) and produce EM waves with the same frequency as the AC (alternating current)
- these waves travel through the air until they reach a receiver (an aerial)
- the waves are absorbed and the energy carried by the waves makes electrons in the aerial
- these vibrations cause an alternating current to flow in the aerial, which has the same frequency as the radio wave
What is the primary use of radio waves?
- communication - TV and radio
Why can long wave radio be used to transmit radio signals very long distances, even though the transmitter is not in the line of sight of the receiver?
- long wave radio waves diffract (bend) around the curved surface of the Earth
- they can also bend around hills and into tunnels
How are short and medium wave radio transmitted around the Earth?
- they are reflected off the ionosphere (a charged layer of the upper atmosphere)
Give a use of shortwave radio
- bluetooth = which can send data over short distances between devices
Why do we ‘lose reception’ on a car radio on a long journey?
- FM radio uses shorter wavelength radio waves
- the signal cannot bend round the Earth’s surface or hills and buildings
- as the car moves further away from the transmitter, the signals will be blocked by obstacles
State 2 uses of microwaves
- satellite communication and cooking food
Describe the role of satellites in communication using microwaves
- the signal from a transmitter is transmitted into space and received by a satellite in orbit
- the satellite then transmits the signal back to the Earth’s surface in a different direction, where it is received by a satellite dish on the ground
Describe what happens to microwaves when they reach the ionosphere
- they pass through, into space (where the satellites are in orbit)
Describe the energy transfers involved in heating food in a microwave
- energy is transferred by the microwaves to the thermal store of the water molecules in the food, via the radiation pathway
- the energy then passes from the thermal store of the water molecules to the rest of the molecules in the food, via the heating pathway
Describe how infrared cameras are used by the police to catch criminals in hiding
- the criminal’s body gives off IR radiation (as they are warm)
- the camera detects this radiation and turns it into an electrical signal which is displayed on a screen as a picture
Describe how infrared radiation can be used to heat a room
- hot objects emit IR radiation which is absorbed by objects in the room, transferring energy to their thermal stores
- this increases the temperature of the room
How can light be used to transmit information?
- light rays are reflected along optical fibres for long distances
Why is visible light suitable for transmission in this way?
- light can be refracted enough to keep it inside the narrow fibre
- light is not easily absorbed or scattered as it travels along the fibre
Why are radio waves much less harmful than gamma rays?
- radio waves have a low frequency so do not transfer as much energy as gamma rays
- they also mostly pass through soft tissue without being absorbed
What is meant by the term ‘ionising radiation’?
- radiation which carries enough energy to knock electrons off atoms to make them into ions
What are the main dangers from ionising radiation?
- UV = causes sunburn and premature skin aging
- also can cause blindness and higher risk of skin cancer
- x - rays & gamma rays = causes cells to be destroyed or mutates genes, which can lead to cancer
Why would someone choose to expose themselves to ionising radiation if it can cause cancer?
- sometimes the risk of a person developing cancer is much smaller than the risk to long term health if radiation is NOT used (eg. if a person had injuries which were left untreated because a person refused an x ray)
What is the definition of ‘radiation dose’?
- a measure of the risk of harm from the body being exposed to radiation
The risk of harm from radiation depends on which two factors?
- the amount of radiation absorbed and how harmful that type of radiation is
A patient’s pelvis is being examined. It can either be examined with a single X-ray photograph or a CT scan
An X-ray of the pelvis has a radiation dose of 0.7mSv, whereas a CT scan has a radiation dose of 7mSv
How much larger is the risk of harm if the patient has a CT scan?
70/ 0.7 = 10
- the CT scan carries a risk of harm 10 times higher than an X ray
What are the main uses of ultraviolet radiation?
- fluorescent lights, security pens and sun beds
How do fluorescent lights work and why are they useful in schools & offices?
- they generate UV light
- the inside of the bulb is coated with a phosphor layer which absorbs the UV and re-emits it as visible light
- they are useful as they are very energy efficient
Describe how fluorescence is also useful in security pens
- your property is marked with a security pen which is invisible in normal light conditions
- if the police discover stolen property, they shine a UV light on it and the ink will fluoresce, so the property can be identified
How are gamma rays used in radiotherapy?
- beams of gamma rays are directed at cancerous cells in order to kill them
Why is gamma radiation suitable to use a medical tracer?
- because it can pass through the body to be detected outside the body
- gamma radiation is also less ionising than alpha and beta radiation
Why do radioactive isotopes tend to collect around a tumour so they can be detected?
- tumours are cells which are dividing out of control
- this means they need a good blood supply to get nutrients
- a tracer injected into a patient will be carried to the tumour in the blood
Describe an important consideration when deciding which radioactive substance to inject into a patient to be used as a tracer
- it needs to have a short half life so it will decay quickly and not contaminate the patient’s body for too long
What precautions are taken by medical staff working with radioactive sources?
- they wear lead aprons, stand behind screens or leave the room during the procedure
- hospital staff also wear special badges, designed to check that they have not received too large a radiation dose
Why are these same precautions unnecessary for patients?
- they are only exposed to a small dose so the risk of harm is small, rather than working with radioactive sources all day
