1
Q
What are sound waves?
A
- Type of longitudinal wave that passes through the surrounding medium as a series of compressions and rarefactions-vibrating
- an objects size, shape and structure determines which frequencies of sound it transmits
2
Q
What happens as sound travels through different mediums?
A
- if it changes speed and frequency remains fixed, the wavelength changes as velocity=frequency x wavelength
- gets longer as it speeds up and shorter as it slows down
- faster in solids than liquids and in liquids than gases
3
Q
What are stages 1 and 2 of hearing?
A
- sound waves reach your ear drum causing them to vibrate
- vibrations are passed onto ossicles through the semi circular canal to the cochlea
4
Q
What is stage 3 of hearing and how it is limited?
A
- cochlea turns these vibrations into electrical signals which are sent to your brains which interprets then as different pitches and volumes based of their frequency and intensity
- sound is limited by size, shape and structure of the eardrum
5
Q
What is ultrasound?
A
Sound with frequencies higher than 20,000Hz
6
Q
How can ultrasound be made?
A
Electrical devices can be made that produce electrical oscillations of any frequency which can be converted into mechanical vibrations to produce ultra sound waves
7
Q
How is ultrasound used for foetal scanning?
A
- ultrasound passes through the body but whenever they reach a boundary between two media some of the wave is reflected back and detected (e.g. fluid of the womb and skin of foetus)
- the exact timing and distribution of these echos are processed by a computer to produce a video image
8
Q
How is ultrasound used for sonar?
A
- used by boats and submarines to find the distance to the seabed or to locate objects in deep water
- the time between a pulse of sound being transmitted and detected and the speed of sound in water can be used to distance of the surface or object -echo sounding
9
Q
What is infrasound?
A
Sound with frequencies lower than 20Hz
10
Q
How is infrasound used for exploration of the earth’s core?
A
- earthquakes produce seismic waves at a range of frequencies (some beneath 20Hz) and can be detected all across the earth
- seismologists work out the time these waves take to be received to explore the structure as different densities in the core result in absorption and refraction
11
Q
What is fission?
A
- a type of nuclear radiation that is used to release energy from atoms
- when a large atom splits into two smaller atoms (daughter nuclei) and three neutrons and energy
- the products of fission are radioactive
12
Q
How does fission start and continue?
A
- started by an incident neutron as it is absorbed by the main atom making it more unstable
- by having neutrons left at the end they can induce fission in other atoms causing them to split creating a chain reaction
13
Q
How does fission work in a power station?
A
- energy released by fission is transferred to the thermal energy store of the moderator causing it to heat water in the boiler
- this produces steam and energy transferred to KE as it rises
- this turns a turbine transferring KE which turns a coil of wire within a magnetic field creating a current and electricity
14
Q
Why does fission have safety controls?
A
If the chain reaction is left unchecked, large amounts of energy are released in a short period of time and lots of fission causing a runaway reaction and potential explosion
-nuclear power stations produce controlled chain reactions
15
Q
What does the moderator do?
A
- usually graphite
- moderators with fuel rods slow neutrons down so they can be absorbed
16
Q
What do control rods do?
A
- usually boron
- limits the rate of fission by absorbing excess neutrons so only one neutron produces more fission control the reaction
- if temp is too high move control rods down, too low move them up
17
Q
What is fusion?
A
- two light nuclei collide at high speed and temperature, fusing to create a larger heavier nucleus and energy
- the heavier nucleus doesn’t have as much mass as the two lighter nuclei as some mass is converted into energy and carried away by radiation
18
Q
Where does fusion happen naturally?
A
On the sun and stars providing them with energy
- this is how all elements other than hydrogen were created
- we don’t tend to used it on earth as the amount of energy put in isn’t viable with the amount we get out as we have less fuel than the sun
19
Q
Why does fusion need the conditions it does?
A
- happens at very high pressures and temperatures (10,000,000)
- because positively charged nuclei have to get very close to fuse so the strong force due to electrostatic repulsion must be overcome
- more kinetic energy means nuclei get closer before this happens
20
Q
What are the pros of fusion?
A
- doesn’t release CO2 so is a clean source of energy
- Huge amount of energy can be created from small nuclear material
- very reliable
- generally pretty safe with little waste
21
Q
What are the cons of fusion?
A
- public perception is of it being very dangerous
- if waste products leak they can contaminate natural sources for years due to long half lives and cause explosions
- High overall costs both initially and when decommissioning p
22
Q
What is pressure?
A
The force per unit area
Pressure = Force on a surface /area of that surface
23
Q
What creates pressure?
A
As gas particles move around at high speeds they bang into each other exerting a force as they collide -fluid pressure
24
Q
What effect does temperature have on gas pressure?
A
- the speed of gas particles increases as the temperature gets higher as the more frequently particles collide
- the force exerted by each particles also increases
- so increasing temperature of a fixed volume of gas increases pressure
25
What effect does volume have on pressure?
If temperature is constant, if volume of gas increases gas pressure decreases as particles are more spread out so collide less frequently
-pressure and volume are inversely proportional
26
What is the estimated distance required for a road vehicle to stop at
- 30mph
- 50mph
- 70mph
- 23m
- 53m
- 96m
27
What effect does speed have on stopping distance?
- as speed increases thinking distance does at the same rate, this is because reaction times stay similar but the higher speed the further you go in that time so braking distance increases
- breaking distance and speed have a squared relationship, is speed doubles breaking distance increases by factor 4 etc.
28
How do cars avoid accidents?
- drivers must leave enough space in front so they can stop safely (at least equals to the stopping distance of their speed)
- speed limits are therefore also important as this increases braking distance
29
What is the equation that occurs as a car stops?
Energy in the cars kinetic energy store = work done by the breaks
1/2 x m x v squared = f x d
-this is because energy is transferred from the kinetic energy store to the thermal energy store of the brakes
30
What happens when a wave is reflected, absorbed and transmitted?
- reflection =The incoming ray is ‘sent back’/repelled away from the second material
- absorption =the wave transfers energy to the material’s energy stores
- transmitted = the wave carries on travelling through the new material which often leads to refraction
31
What happens when a wave is refracted?
- if a wave hits the boundary at an angle the change in speed due to a different material causes a change in direction - refraction
- the greater the change in speed the more it bends, bending towards the normal if it slows down and away from the normal if it speeds up
32
What happens when EM waves are refracted?
- usually travel slower in denser materials
- how much EM wave is refracted can be affected by its wavelength as shorter wavelengths bend more which can lead to dispersion
33
What is specular and diffuse reflection?
- specular is when waves are reflected in a single direction by a smooth surface so you get clear reflection (produces a virtual image upright)
- diffuse reflection occurs when waves are reflected by a rough surface in all direction as the normal is different for each Ray so they have different angle of incidence (this can cause a distorted image or none at all)
34
What is the law of reflection?
Angle of incidence = angle of reflection
35
What is total internal reflection?
- happens when the angle of incidence is larger than the critical angle for that material
- all incoming rays are reflected none are refracted, can only happens when travelling from a dense material to a less dense one
- if angle of incidence = critical angle it will be refracted along the boundary
36
What is the power of a lens dependent on?
-the more powerful the lens the more strongly it converges rays of light so the shorter the focus length
(Converging lens has positive power as ray energy has a cumulative effect, diverging lens has negative as principle focus energy diverges)
-the more curvature an object has the higher the power is
37
How is colour of light related to different absorption of surfaces?
- different materials absorb different wavelengths of light
- this is because it absorbs all wavelengths of light expect the colour it is which it reflects (e.g. red apple reflect red light)
- all colours other than primary can also be made by mixing colours (e.g. yellow objects may reflect blue and green)
38
What are opaque, white, black and translucent/transparent objects?
- opaque objects absorb some wavelengths of light and reflect others
- white objects reflect all wavelengths of light equally
- black objects absorb all wavelengths of light
- translucent/transparent transmit light
39
How does colour of light depend on transmission through filters?
- colour filters are used to filter out different wavelengths of lights only certain colours are transmitted and the rest absorbed
- primary colour filters only transmit that colour, if the object was a different colour If would appear black through a primary colour filter as all of the light would be absorbed
- non-primary colour filters let through all wavelengths of light that correspond to that colour
40
What is a converging lens?
- Bulges outwards in the middle (convex)
- it causes parallel rays of light to converge at the principle focus
- the principle focus of this lens is where rays hitting the lens parallel to the axis appear
- real, upside down/or upright, magnified or not
41
What is a divergent lens?
- caves inwards (concave)
- cause parallel rays of light to spread out
- the principle focus of a diverging lens is the point where rays hitting the lens parallel to the axis appear to all come from
- virtual, diminished, upright
42
What is the focus length and axis?
- focus length is the distance from the centre of the lens to the principle focus
- axis is a line passing through the middle of the lens
43
What is a real image?
Images are formed at points where all the light rays from a certain point on an object appear to come together
-real images form when the light rays actually come together to form an image. This can be captured on a screen as the images actually meet at the place where the image seems to be
44
What are virtual images?
When light rays from the object appear to be coming from a complete different place to where they’re actually coming from.
-They don’t actually converge at the appeared image point so cannot be captured on a screen
45
What does the amount of radiation a body emits depend on?
The distribution and intensity of these wavelengths only depends in the object’s temperature (intensity = power per unit area)
-as the temperature of an object increases the intensity of every emitted wavelength increases, this increases more rapidly for shorter wavelengths causing the peak wavelength to decrease
46
How does a body reach a constant temperature?
- for an object to maintain a constant temperature is must absorb and emit the same average power (amount of radiation)
- if it absorbs more it will heat up, emits more it will cool down
47
How is the earth affected by factors controlling the balance of radiation?
Depends on the amount of radiation it absorbs, reflects and emits
- during the day it absorbs lots of radiation and reflects some as lots or radiation is transferred from the sun increasing temp
- at night more radiation is emitted causing a decrease in temp
- Therefore overall remains roughly constant
48
How is alpha radiation used for fire alarms?
- a weak source of alphas radiation is placed on a smoke detector close to two electrodes
- the source causes ionisation and a current to flow
- if there is a fire then smoke will absorb the radiation stopping the current so the alarm sounds
49
How is gamma radiation used to irradiate food and sterilise medical equipment?
-kills microbes on food so it doesn’t go bad as quickly and sterilises equipment so can be used on other patients and doesn’t spread disease
This is good as it doesn’t involve boiling so they are sterilised without damage
-sources needs to be strong with a reasonably long half life
50
How is beta radiation used for measuring paper thickness?
- you direct radiation through the stuff being made and place a detector on the other side connected to control units
- when the amount of detected radiation changes it means the paper is coming out too thick or too thin so control units adjust the rollers
- must be beta sources as the paper will partially block the radiation, if not then the reading won’t change as all radiation will pass through
51
How is radiation used for tracers?
A medical beta or gamma tracer is injected or swallowed by a patient and its progress around the body is followed using an external detector. E.g. may emit gamma rays
-sample must be gamma or beta so that it passes out of the body without doing too much damage
52
Why is radiation dangerous?
- can enter living cells and ionise atoms and molecules within them leading to tissue damage
- lower doses tended to cause minor damage without killing the cell giving a rise to mutant cells which divide uncontrollably -cancer
- higher doses tend to kill cells completely leading to radiation sickness
53
What radiation is most dangerous?
- outside the body beta and gamma are the most dangerous because they can penetrate through skin and damage delicate organs, alpha is less dangerous as can’t penetrate through skin
- inside he body alpha sources are the most dangerous as they are strongly ionising so can do lots of damage in a localised area (contamination rather than irradiation is the major concern with alpha)
54
What is internal radiation therapy?
- a radioactive material is placed inside the body or near a tumour through injecting or implanting
- alphas is usually injected near the tumour as is highly ionising so can do lots of damage in a nearby area and damage to normal tissue is limited as they have a short range
- beta is usually implanted (inside or next to) as can penetrate the casing of the implant before damaging cancer cells
55
Why is the half life of radioactive sources used in internal treatment short?
To limit the time that a radioactive substance is inside the patients body and therefore danger
56
What is external radiation therapy?
- gamma rays (this can be serval static beams or one concentrated beam) aimed and carefully focused at the tumour as they can penetrate through skin (shielding may be used on other areas yet damage is still dome to healthy cells)
- the sources used should have long half lives so they don’t have to be replaced often (sources are often shielded and keep separate to reduce rick to patients and staff)
57
What is PET scanning?
A technique used to show tissue or organ function, it can also be used to diagnose medical conditions e.g. cancer
58
What are stages 1,2 and 3 or PET scanning?
- beta plus source attached to a glucose molecule
- inject the radioactive molecule into the patient
- the radioactive molecule travels to a place where lots of respiration is taking place (high metabolic activity e.g. cancer as growing a lot so take up more)
59
What are stages 4,5 and 6 of PET scanning?
- positron is emitted by the radioactive molecule and annihilates with electrons in an organ
- the annihilation produces 2 gamma rays in opposite directions which are detected by a ring detector to produce a 3D image whereby the tumour will lie along the same path as each pair
- by detecting three pairs the tumour can be accurately located through triangulation
60
What are the isotopes used in PET scanning like?
-have short half lives so radiation isn’t in the body for too long and so their activity isn’t too low and no longer useful when they arrive. this means they are made close to where they’re used
61
What medium can P waves and S waves travel through?
- p waves can travel through both solids and liquids
- S waves can only travel through solids
- p waves travel faster than S waves
62
What is the equation for lens power?
Power (diotrope, F)= 1/ focal length(m)
63
What happens for images and focal lengths?
If the light rays comes from a distant object the image always forms at the focal length
-if the object is closer to the lens than the focal point it won’t form here
64
How do you calculate distance from lens the image will form at?
1/f = 1/u + 1/v
F=focal length
U =object distance
V=image distance
65
How do you calculate distance from lens the image will form at?
1/f = 1/u + 1/v
F=focal length
U =object distance
V=image distance
66
What happens to person before PET scan?
They must relax first so sit there for like an hour so their muscles aren’t respiring much and so lots of radiation doesn’t go to these areas
Physics
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