PAPER 4 Flashcards
1
Q
What is a wave?
A
an oscillation that transfers energy
2
Q
What are sound and water waves?
A
- mechanical waves
- need a medium (matter) to travel through unlike electromagnetic waves
3
Q
What are longitudinal waves?
A
- soundwaves
- direction of vibration of individual air molecules is the same as the direction of the wave
4
Q
What are transverse waves?
A
- direction of vibration is at right angles to the direction of travel of the wave
- if you make a transverse wave on a spring, the individual coils move up and down, but the energy is transferred horizontally
- ripples on water
5
Q
What is amplitude?
A
- distance from the middle to the top (crest) or bottom (trough) of a wave
6
Q
What is wavelength?
A
- distance from one point on a wave to the same point on the next wave
- metres
7
Q
What is frequency?
A
- number of waves, or oscillations, per second
- Hz, hertz
8
Q
What is the time period?
A
- the time for one wave to pass a given point
- seconds
9
Q
apply formulae relating velocity, frequency and wavelength
A
wave velocity (m/s) = frequency (Hz) x wavelength (m)
10
Q
Describe absorption of wave energy
Provide 3 examples
A
Common examples of absorption of wave energy:
- waves hitting the beach usually give most of their energy to the sand
- sunlight landing on a face is mostly absorbed, warming the skin
- sound waves hitting thick curtains give up their energy and the sound is muffled
11
Q
Describe transmission of wave energy
Provide 3 examples
A
Common examples of transmission of wave energy:
- sea waves passing a shallow area continue with their energy mostly unchanged
- light passing through a glass window continues with over 95% of its energy
- ultrasound waves scanning a baby pass from flesh into bone and continue with enough energy for the machine to detect the echo
12
Q
Describe reflection of wave energy
A
an echo
13
Q
What is ultrasound?
A
- a sound of a frequency greater than 20,000 Hz
- has a very small wavelength, so it can be focused into a beam
- a transmitter beams ultrasound waves into the mother
- the waves reflect from the different boundaries
- the machine calculates the distances using time and velocity, and uses those distances to produce an image
14
Q
Describe the ear
A
- designed to detect, amplify and convert sound into an electrical signal
- sound waves enter the ear canal and cause the eardrum to vibrate
- three small bones transmit these vibrations to the cochlea, which produces electrical signals which pass through the auditory nerve to the brain, where they are interpreted as sound.
15
Q
Why does hearing (audition) change due to aging?
A
- hairs in cochlea have a natural frequency
- if a vibration is applied to cochlea hair at their natural frequency, they will vibrate with a very big amplitude (resonance)
- hair in the cochlea have different lengths and resonate at different frequencies of sound
- range of frequencies you can hear depend on the range of lengths of hair in your cochlea
- as you age, the hair in the cochlea get shorter, making it more difficult to hear higher frequencies
16
Q
What are electromagnetic waves?
A
- transverse
- are transmitted through space where all have the same velocity
- transfer energy from source to absorber (some transfer information, eg. microwaves sent to satellites)
- consist of oscillating electric and magnetic fields
17
Q
Outline the electromagnetic spectrum
A
Radio-waves Micro-waves Infrared Visible light Ultraviolet X-rays Gamma Rays
R-G = decreasing wavelength and increasing frequency
18
Q
Give examples of some practical uses of electromagnetic waves
A
Microwaves = communication with satellites, WiFi and bluetooth
Radio waves = TV and radio stations (add sound and picture information to radio waves)
Infrared - remote controls to televisions via pulses & cooks food in an oven/grill
Micro wave - in a microwave, the water and fat in food absorb the microwaves, which heats up the outside of the food (conduction transfers energy to the middle)
Visible light - lasers in CDs, DVDs, and Blu-ray disks
Ultraviolet - helps to produce vitamin D (strong bones) & helps to detect forged bank notes
19
Q
How can ultraviolet be potentially hazardous?
A
- can damage or kill cells
Good:
- kills bacteria in water (sterilises it)
Bad:
- can damage DNA in skin cells (cells may grow rapidly and cause skin cancer)
- ultraviolet exposure can cause cataracts, which makes corneas cloudy
20
Q
How can X-rays be potentially hazardous?
A
- can damage or kill cells
Good:
- can kill skin cancer or other cancer cells
Bad:
- can damage your cells and cause cancer
- a radiographer operating on an X-ray machine stands behind a lead screen or in another room whilst the machine is on
21
Q
How can gamma rays be potentially hazardous?
A
- can damage or kill cells
Good:
- can kill cancer cells
- can kill bacteria on food
Bad:
- can damage or kill the cells in your body
22
Q
How are infrared waves used for medical imaging?
A
- A thermal imaging camera produces a thermogram (an image that shows regions of different temperatures) (thermograms can show problems with blood flow in blood vessels)
- Pixels inside a CCD (charge-coupled device - eg. A phone camera) absorb infrared and produce an image
- Colours are added by a computer
- Skin will emit more infrared radiation if it is hot due to injury or infection
23
Q
How are X-rays used for medical imaging?
A
- Bones absorb many X-rays (soft tissues such as skin and muscle do not)
- Photographic film darkens when it absorbs X-rays and shows the details of a person’s internal structure
- A CCD (charged-coupled device) can detect X-rays
- Colours on an X-ray show differences in intensity due to different densities of the material that the X-rays have travelled through (higher density material = absorbs more X-rays)
- Computerised tomography = when a computer uses X-rays to make an image that looks like a slice through your body = produces CT scans
24
Q
How are gamma rays used for medical imaging?
A
- used as tracers to treat problems with organs
- tracers are also used to find leaks in underground pipes (more gamma rays will be detected from a point above a leak than in the rest of the pipe)
- a doctor injects a patient with a tracer (a radioactive substance that emits gamma rays)
- patient’s organ absorbs the tracer
- the doctor diagnoses problems from the CCD images
25
What is the relationship between radio waves and oscillations?
radio waves can be produced by, or can themselves induce, oscillations in electrical circuits
26
How do different substances absorb, transmit, refract, reflect electromagnetic waves?
different substances may absorb, transmit, refract, or reflect electromagnetic waves in ways that vary with wavelength
27
Why are electromagnetic waves refracted?
- when an electromagnetic wave goes from air to a denser medium at an angle, it slows down and bends towards the normal
- larger difference in density = larger change in direction
28
Why are electromagnetic waves reflected and refracted?
- earth is curved
- if you want to send radio waves over very long distances, you reflect them from the ionosphere (a layer of the atmosphere)
- high-frequency radio waves, or micro waves have a smaller wave length so you can use them for satellite communication
29
Why are electromagnetic waves transmitted and absorbed?
- depends on wavelength
30
Describe a convex lens
- magnifying
- refracts rays to a principal focus or focal point
- focal length = the distance from the optical centre of the lens to the focal point, when the rays going into the lens are parallel
31
Describe a concave lens
- spreads light out
- cannot set fire to anything
- fixes short-sightedness
32
How do you construct a ray diagram?
- shows what happens when electromagnetic waves hit a surface or travel through matter
1. Draw lines to represent the rays
2. Draw a normal at 90o to the surface at the point where the ray hits it
3. Measure the angles from the normal to the rays
33
explain how colour is related to differential absorption, transmission and reflection
- each frequency of light travels at a slightly different speed in glass
- each frequency of light is refracted by a different amount
- colours with a higher frequency are refracted at greater angles (this spread light out into a spectrum - dispersion)
- light can be scattered from particles (why milk appears white bc. the particles scatter all wavelengths) (ink appears black bc. particles absorb all wavelengths)
- specular reflection - regular surface reflection (mirror)
34
What is an isotope?
atoms of an element with different numbers of neutrons
35
What do unstable nuclei emit?
Radioactive decay
36
What is alpha radiation?
- particle
- nucleus of a helium atom
- 4 2 He (equation symbol)
- large relative mass
- +2 charge
- high ionising power
- short penetrating distance
37
What is beta radiation?
- particle
- a fast-moving electron
- 0 -1 e (equation symbol)
- a neutron can decay to make a proton and an electron
- small relative mass
- -1 charge
- medium ionising power
- medium penetrating power
38
What is gamma radiation?
- electromagnetic wave
- no equation symbol
- no relative mass
- no charge
- low ionising power
- long penetrating power
39
What is neutron radiation?
- a particle in the nucleus
| - 1 0 n (equation symbol)
40
What is ionising radiation?
- the radiation emitted by a radioactive material
- can remove electrons from atoms to produce positively-charged ions
- must transfer energy to an atom to ionise it
41
Why do atoms emit radiation?
- Electrons can be 'excited' by many things - eg when passing an electric current through an atom of gas
- when electrons move from a higher to a lower energy level, they emit radiation
- an emission spectrum = shows a set of frequencies of radiation emitted by an atom when excited electrons move to lower energy levels
- frequency of radiation emitted depends on the difference in energy of the energy levels
- energy change can take place in one go or two or more
- 2 changes = emitted photons will have less energy, lower frequencies and longer wavelengths
- largest energy difference = from an energy level just below ionisation
- highest energy photons from a hydrogen atoms are in the ultraviolet part of the electromagnetic spectrum, but carbon atoms can emit X-ray photons
- Gamma rays = highest energy radiation = emitted from nuclei
- Protons and neutrons occupy energy levels in the nucleus & energy levels = much higher so radiation emitted is of a higher energy
42
How are electrons in atoms arranged?
- different atoms have different energy shells
- electrons usually occupy the lowest possible energy level at the smallest distance from the nucleus
- inner electrons can become 'excited' when they absorb energy from radiation, and rise to a higher energy level
- when this energy is lost by the electron, it is emitted as radiation
- when outer electrons are lost = ionisation
43
What happens when atoms absorb electromagnetic radiation?
PHOTON MODEL
- electromagnetic radiation = emitted and absorbed as packets of energy (photons)
- energy of each photon = proportional to the frequency
- only a photon of exactly the right energy can 'excite' an electron to a higher energy level
- when light of all frequencies is passed through hydrogen gas, some frequencies are absorbed
- an absorption spectrum = shows a set of frequencies of radiation absorbed by an atom when excited electrons move to higher energy levels
- only a photon that has enough energy can completely remove an electron from the atom = the atom is ionised - photons of ultraviolet, X-ray and gamma ray frequencies have enough energy to ionise atoms
44
What is a half-life?
- the time it takes for half the unstable nuclei to decay, or for the activity to halve
- atoms decay; they do not disappear (if they emit alpha or beta particles, they change to the atoms of a different element, and eventually become stable
45
How do you measure the activity of a radioactive material?
- random decay
- Geiger counter (measures the activity, ie count rate)
- activity = radiation (photons or particles) emitted per second
- activity = measured in becquerels (Bq)
46
What is irridation?
- happens when there is radioactive material outside your body but it can travel into your body
- ionising radiation can damage the DNA in your cells, which can cause cancer
- your body can repair any damage from small doses of radiation, but too much exposure increases the risk of cancer
47
What is contamination?
- happens when you take radioactive material inside your body or if it is on your skin
- once you are internally contaminated, you cannot remove the radioactive material from inside you
- ionising radiation can damage the DNA in your cells, which can cause cancer
- your body can repair any damage from small doses of radiation, but too much exposure increases the risk of cancer
48
explain why the hazards associated with radioactive material differ according to the half-life involved
- Doctors may inject a patient with a radioactive isotope that is absorbed by the organs of your body, and detected by a gamma camera.
- The camera makes images of your organs, which helps doctors to diagnose disease.
TOO SHORT
If the half-life of the isotope is too short, then the tracer will decay before they can use the gamma camera.
TOO LONG
If the half-life is too long, then the tracer will continue to emit radiation for a long time and increase the risk of cancer.
49
What is nuclear fission?
- "The splitting of a nucleus into 2 smaller nuclei, with the release of energy and neutrons".
- for fission to occur the unstable nucleus must usually first absorb a neutron
- Unstable nuclei have too much energy, due to an imbalance between the number of protons to neutrons.
- Such nuclei will undergo radioactive decay.(emit α, β and/or γ radiation)
- Such unstable nuclei are naturally occurring.
- Stable nuclei can be made unstable by adding neutrons to them.
- If large nuclei are made unstable, they have so much instability, they simply break apart.(as opposed to emitting α, β and/or γ)
- In a nuclear reactor, fission is induced when a Uranium-235 nucleus is hit with a neutron.
- The two smaller nuclei (daughter nuclei) are themselves unstable, and become stable by undergoing radioactive decay(emit α, β and/or γ radiation)
- nuclear waste = very dangerous, has very long half-life & must be buried and guarded
50
Are all nuclei stable?
- some nuclei are unstable and may split
- a nucleus is unstable if it has different numbers of protons and neutrons
- unstable nuclei will decay and emit radiation = radioactive decay
- radioactive decay = spontaneous & random
51
What is a chain reaction (fission)?
Process in which neutrons released during a fission event, go on to produce further fission events
52
What is a controlled chain reaction (fission)?
Nuclear Power
- Only one neutron from each fission event is able to produce another fission event.
- Control rods in power plants absorb surplus neutrons and energy is generated at a steady rate.
53
What is an uncontrolled chain reaction?
Neutron bomb
Every neutron from each fission event goes on to produce further fission events.
Energy is released at an exponential rate.
54
What is Einstein's mass-energy equivalence equation?
A tiny difference in mass results in large release of energy.
E=mc^2
Energy (joules) = change in mass (kg) x speed of light (3x10^8 m/s) ^2
55
Describe the process of nuclear fusion
knowledge that mass may be converted into the energy of radiation
- "The joining of two small nuclei to form a larger nucleus, releasing energy".
- Occurs in stars when 2 very light nuclei (isotopes of Hydrogen) are forced together at high speeds, to form heavier Helium or Hydrogen nucleus (isotopes) .
- There is a difference in mass (not number!) between nucleons in the hydrogen nuclei and the helium nucleus they fuse to form.
- The helium nucleus has less mass than the sum of the masses of the hydrogen nuclei.
- The "missing mass" is transformed into energy by Einstein's mass-energy equivalence equation.
56
What are the advantages of nuclear fusion?
1) No radioactive waste produced (unlike fission which has a very long half-life radioactive waste)
2) The fuel required for fusion is readily available in water.(unlike fission, which uses uranium which is non-renewable)
3) Nuclear fusion produces a lot more energy than fission (four times as much than fission)
57
What are the disadvantages of nuclear fusion?
Building fusion reactors is very difficult/not viable.
- Currently, more much heat energy required to make nuclei to overcome their repulsive forces and fuse than is released from fusion!
- need cleverer method of fusing nuclei.
- Stars are able to carry out fusion easily as they have very high temperatures and very high pressures.
58
How is energy transferred?
1) Mechanically - force doing work
2) Electrically - work done by moving charges OR electrical current
3) Heating by particles
4) Heating by radiation
59
What is the equation for mechanical energy transfer?
work done (J) = force (N) x distance (m)
60
What is the equation of electrical energy transfer?
energy transferred = electrical power x time
61
What is the equation for thermal energy transfer?
change in thermal energy = mass x specific heat capacity x change in temperature
62
What is the law of conservation?
- no net energy change in a closed system
| - energy cannot be created or destroyed; can only be transferred between stores
63
Describe energy transfer for domestic appliances
- from a chemical store in a battery
- from a chemical or nuclear store of the fuel in a power station used to produce mains electricity
- Kilowatt-hour is unit used for domestic appliances
64
What is a kilowatt-hour?
- energy transferred by a 1 kW appliance switched on for an hour
electrical work done (kWh) = power (kW) x time (h)
power = electrical work done / time
65
How can you reduce dissipated energy?
- reduce energy dissipated due to friction by lubrication
| - reduce energy dissipated due to heating by insulation
66
What does thermal conductivity mean for a room?
It will cool down faster
- thermal conductivity tells you how quickly energy is transferred through a wall with:
- an area of 1m2
- a thickness of 1m
- a temperature difference across it of 1oC
67
calculate the amounts of energy associated with a moving body, a stretched spring and an object raised above ground level
```
For an object raised above ground level:
potential energy (J) = mass (kg) × height (m) × gravitational field strength (N/kg)
```
```
For a moving object:
kinetic energy (J) = 0.5 × mass (kg) × (speed)2 (m/s)
```
For a stretched spring:
energy transferred in stretching (J) = 0.5 × spring constant (N/m) × (extension)2 (m)
68
What is the equation for energy efficiency?
efficiency = useful output energy transfer / input energy transfer (or total energy transferred)
- no appliances are 100% efficient because energy is always dissipated
69
describe ways to increase efficiency
- use insulation to reduce heating of the surroundings
- make devices from material that reduce unwanted energy transfer
- use technology to produce devices that are better at their job (eg. LEDs)
- more efficient devices operate at a lower power (use up fuels more slowly)
70
recall typical speeds encountered in everyday experience for wind and sound, and for walking, running, and cycling
```
strong wind = 13 m/s
sound = 330 m/s
walking = 1 m/s
running = 5 m/s
cycling = 7 m/s
```
71
What is reaction time?
The time taken to respond to a stimulus.(about 0.2 seconds)
72
What is thinking distance?
thinking distance = time take for driver to actually do something (eg press the brakes)
thinking distance = speed x time
thinking distance is affected by:
- drinking alcohol
- using drugs (as, well as some medicines)
- being tired
- age (reaction time decreases as you get older)
- distraction (by other people in car, gps or by eating/drinking)
73
What is braking distance?
the distance travelled by the vehicle in the time the brakes act
- depends on the brakes and the surface that is being driven on (does not depend on the driver)
74
What is stopping distance?
Stopping distance = thinking distance + braking distance
75
explain the dangers caused by large decelerations
- seatbelt exerts a force on you if car slows down suddenly (to stop you from colliding with the dashboard or the seat in front)
- seatbelts must be replaced after an accident because they stretch
- seatbelt can cause compression injuries
- can injure internal organs because they continue to move inside your body even if the ribs are stopped by the seatbelt
76
What is nuclear fuel?
- non-renewable energy source
- eg uranium
- formed in stars
77
What are fossil fuels?
- non-renewable energy source
- eg coal, oil, gas
- formed form the effects of heating and pressure on the remains of wood and sea creatures over millions of years
78
What is biofuel?
- a renewable energy source
| - comes from living material (eg wood, ethanol from sugar, or methane from sewage)
79
What is wind energy?
- turbines and generators
| - renewable energy source
80
What is hydroelectricity?
- water high up
| - renewable energy source
81
What is tidal energy?
- renewable energy source
| - turbines and generators driven by the waves
82
What is solar energy?
- renewable energy source
| - solar panels
83
What happens in the national grid?
electrical power is transferred at high voltages from power stations, and then transferred at lower voltages in each locality for domestic use
84
What are step-up and step-down transformers used for?
- to change the potential difference as power is transferred from power stations
- reduces the heating effect, making the National Grid more efficient
85
What are the issues with energy supply?
- cost (to set up, and to remove)
- effect on the environment
- contribution to climate change
- how long the sources will last
86
What is direct voltage?
- a potential difference that does not change direction (eg from a battery)
87
What is alternating voltage?
- a potential difference that changes direction, usually described as positive and negative
88
link the potential differences and numbers of turns of a transformer to the power transfer involved
Potential difference across primary coil x current in primary coil = potential difference across secondary coil x current in secondary coil
Primary voltage / secondary voltage = number of turns on primary coil / number of turns on secondary coil
89
What is the domestic supply in the UK?
- generators in power stations produce an a.c. at 50 Hz and about 230 volts
90
What is the function of live mains wire?
- live wire (brown) and neutral wire (blue) make a complete circuit with appliance
- Carries the alternating potential difference from the supplier to the appliance
91
What is the function of neutral mains wire?
- live wire (brown) and neutral wire (blue) make a complete circuit with appliance
- Completes the circuit. The neutral wire is at 0 V (earth potential).
92
What is the function of earth mains wire?
- green and yellow
- not connected to the mains
- connected to 'Earth', which is usually a large metal pole buried in the ground outside your house
- connects metal casing to the pile so current flows through the Earth wire, not through you (Earth wire has less resistance than you)
- Earth wires are at 0 V
- safety wires, and only carry a current if there is a fault and the appliance has become live (electrified).
93
What are double-insulated appliance?
- have a plastic casing, instead of metal
- no current can flow through the car to you
- do not need to use the Earth pin
94
explain why, if two resistors are in series the net resistance is increased, whereas with two in parallel the net resistance is decreased (qualitative explanation only)
In a series circuit, the total resistance across all of the components (the 'net resistance') increases as more components are added (resistors have same current but different potential difference)
In a parallel circuit, the net resistance decreases as more components are added, because there are more paths for the current to pass through (resistors have different current and potential difference)
95
1) If the switch in a mains circuit explain is open, can the live wire still be dangerous?
2) Explain some of the safety measures taken with wires.
Yes, even if a circuit is switched off (ie the switch is open), the live wire can still be dangerous.
If you touch it, you may complete a circuit between the live wire and the earth (because you'll be standing on the floor), so you get a shock.
INCLUDE
Dangers of providing any connection between the live wire and earth
the protection offered by insulation of devices
EARTH WIRE
- The earth wire carries current to the ground (literally, earth).
- This makes circuits safer because if there is a fault, it conducts the current to the ground rather than making the appliance 'live'.
- Appliances become live if the live wire touches the case (particularly a problem with metal-cased appliances, like cookers or toasters)
LIVE WIRE
- Live wire = most dangerous wire because it is at 230 V
- Live wire should never touch the earth wire (unless the insulation is between them, of course!), because this would make a complete circuit from your mains supply to the ground (earth).
- A shock or fire would be highly likely.
96
What is red shift?
- The shift in wavelength of the light from distant stars/galaxies to longer wavelengths
- Implies that distant galaxies/stars are moving away from us
97
What is blue shift?
- The shift in wavelength of the light from distant stars/galaxies to shorter wavelengths.
- Implies that distant galaxies/stars are moving towards us
98
What is evidence for the Big Bang?(1)
| Frequency & Wavelength
- Light from distant galaxies is red-shifted.
- The further away the galaxy, the greater the red-shift.
THEREFORE
- Galaxies are moving away from us.
- The further away the galaxy, the faster it is moving away
CONCLUSION
- Thus, if galaxies are moving away from each other, this suggests that at one point, all matter must have been existed at a single point in space
EXPLANATION
- A spectrum is the range of wavelengths (colours)observed when light from a source is separated into its separate wavelengths.
- White light and light from stars passing through a prism produces a "rainbow" spectrum.(white light contains all wavelengths of light)
- The spectra of stars contains black lines.
- These black lines correspond to very specific wavelengths of light absorbed by certain atoms in the star
- All stars contain Hydrogen and Helium atoms.
- Hence all spectra from stars contain a series of very specific black lines (distinct pattern of separated lines)
- These black lines are seen shifted in the spectra from distant stars towards longer wavelengths.
- This implies that light from distant stars has undergone a Doppler shift
99
What is evidence for the Big Bang?(2)
| CMBR
- The Red-shift of light from distant galaxies alone does not provide complete evidence for The Big Bang Theory
- Up until 1965, a lot of scientists believed the Steady State Theory ("The universe just came into existence and then started expanding") to correctly explain the expanding universe as seen by the red-shift.
- Then Cosmic Background Radiation (CMBR) was discovered.
- At the beginning of the universe, all the energy of the universe would have manifested as very short wavelength gamma waves.
- As the universe expanded, this gamma radiation would have stretched out to longer and longer wavelengths and is now MICROWAVE RADIATION.
- The fact that these microwaves uniformly/evenly fill the universe suggests they all started off from a single point(filling the universe as the universe expanded)
- Steady State Theory cannot explain this fact, only the Big Bang Theory can.
100
What is the Dopplar Effect?
- The physical phenomena by which there is a change in the observed frequency/wavelength of wave, due to relative motion between observer and source.
- It may be that the source and/or the observer is moving
```
WITH SOUND WAVES
When the sound source moves towards you:
- wave peaks move closer together
- wavelength gets smaller
- frequency/pitch of sound increases.
```
When the sound source moves away from you:
- wave peaks move further apart
- wavelength gets bigger
- frequency/pitch of sound decreases.
WITH LIGHT WAVES
- Unlike sound, Doppler effect with light waves is very difficult to observe because light waves have a much smaller wavelength than sound waves.
- Doppler effect is observed when the relative motion between observer and source is very large SO it is observed for distant stars as they are moving very fast
101
What is the lifecycle of a star?
FORMATION
- formed like other stars and planets
- from a huge cloud of dust and hydrogen gas (nebulae)
- gravity pulled the dust and gas together & as that happened, the central core got very hot
- Eventually particles were moving fast enough for nuclear fusion to start
- When enough gas and dust had gathered and became dense enough to start nuclear fusion, a protostar is formed.
- As protostar becomes denser and hotter, particles speed up, collide more energetically and nuclear fusion begins, forming a main sequence star
MAIN SEQUENCE
- A star is stable during its main sequence because there is equilibrium between gravitational attraction (gravitational collapse) and the expansion of the very hot gases outwards due to energy released during fusion
- Nuclear reactions at the centre (or core) of a star provides energy which makes it shine brightly.
- The exact lifetime of a star depends very much on its size.
- Very massive stars use up their fuel quickly SO they may only last a few hundred thousand years
- Smaller stars use up fuel more slowly so will shine for several billion years.
1) Eventually the hydrogen nuclei will run out.
2) star cools, radiation pressure drops
3) gravitational force collapses star, causing it to heat up again
4) fusion of heavier elements begins
- energy from fusion increases
- radiation pressure increases
- star expands outwards becoming either a RED GIANT or a RED SUPER GIANT
THEN - A SMALLER STAR LIKE THE SUN
1) Nuclei for fusion run out
- fusion slows down
- radiation pressure decreases
- gravitational force collapses star
- heats up, becomes white dwarf
- eventually cools down to form black dwarf
THEN - A MASSIVE STAR
1) Lots of heavier nuclei fuse together to release lots of energy = large increase in radiation pressure outwards = much larger than gravitational pull inwards
2) star explodes in a supernova - this scatters materials from inside the star across space, which can collect in nebulae and form the next generation of stars
3) a very dense neutron star forms - these spin rapidly and can give of streams of radiation (pulsars)
4) if neutron star is very dense, it explodes to form a black hole
102
What is the life cycle of a low mass star?
1) Protostar
2) Main-sequence star
3) Red Giant
4) White Dwarf
5) Black Dwarf
103
What is the life cycle of a high mass star?
1) Protostar
2) Main-sequence star
3) Red Supergiant
4) Supernova
5) Neutron Star
6) Black Hole (if neutron star has lots of mass)
104
Why did the Sun start to shine?
Once the Sun became hot and dense enough under gravity, nuclear fusion of nuclei began, releasing energy, causing the sun to emit EM radiation and shine.
105
Why do outer planets have more moons than inner planets?
- Outer planets are larger (have more mass) than the inner planets.
- Thus, their gravitational fields are stronger.
- When the solar system was forming, the outer planets attracted more dust/gas towards them.
- This dust/gas formed came together under gravity to form the many moons of the outer planets.
106
What does the intensity and wavelength distribution of the radiation that all bodies emit depend on?
- temperature
- hot objects can emit a continuous range of electromagnetic radiation at different energy values and therefore frequencies and wavelengths
- a hotter object emits more radiation of a higher frequency (and shorter wavelength) and less radiation of a lower frequency (and longer wavelength)
107
What does the solar system consist of?
The Sun = the star at the centre of the solar system
Planets = objects that are spherical because of gravity, in orbit around the Sun
Moons = objects in orbit around planets
Minor planets = anything that is not a planet or a comet in orbit around the Sun, including asteroids and dwarf planets such as Pluto
Comets = Dust/ice that orbit the Sun with long period, elliptical orbits
4 inner planets
= Mercury, Venus, Earth and Mars = rocky & have an atmosphere
- Atmosphere on Mercury and Mars is very thin
- Atmosphere on Venus is mainly carbon dioxide & it rains sulphuric acid
- Earth has one moon
- Mars has two moons
- Mercury and Venus have no moons
4 outer planets
= Jupiter, Saturn, Uranus and Neptune = all have rings & lots of moons
- Jupiter and Saturn are Gas Giants
- Uranus and Neptune are Ice Giants
- Between Mars and Jupiter, there is an asteroid belt (which contains a dwarf planet called Ceres)
- Asteroids = pieces of rock left over from the formation of the Solar System
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Natural satellites
- moons around planets in the solar system
| - made of the same material as the rest of the objects in the solar system
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Artificial satellites
Have two types of orbits
- geostationary
- low polar
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Geostationary orbit
- 24 hours for one orbit
- about 36,000km above Earth's surface
- remains in a fixed position above Earth's equator
- used for communications and satellite television
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Low polar orbit
- about 2 hours for one orbit
- up to 2000km above Earth's surface
- orbits over the poles
- used for military (spying), observation of Earth and weather
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Explain circular orbits
The gravitational force that acts on any object in orbit always acts:
- towards the centre of the planet
- at right angles to its velocity
The force changes the direction of motion (so it is accelerating), even though its speed does not change
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What must happen for a stable orbit?
Planets are in a stable orbit when they are travelling at the right speed relative to their distance from the Sun
- Gravitational force of the Sun is weaker as you move from Mercury to Neptune
- Neptune moves much slower because there is a small force changing its velocity
If Neptune:
- Sped up, the gravitational force would be too small to keep it in orbit and it would fly off
- Slowed down, it would accelerate towards the Earth
SO IF THE SPEED CHANGES, THE RADIUS MUST CHANGE
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Why must the radius change if the speed changes in order to maintain a stable orbit?
- The closer two objects are to each other, the stronger the force of gravity between them.
- If the force between them is greater, a greater acceleration will occur.
- The greater the acceleration, the greater the change in velocity (this causes the object to move faster)
- This means that objects in small orbits travel faster than objects in large orbits.
- In order to change orbital speed, an object must change the radius of its orbit at the same time, to maintain a stable orbit.
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How is the temperature of a body related to the balance between incoming radiation absorbed and radiation emitted?
Provide everyday examples and the example of the factors which determine the temperature of the Earth
Earth's atmosphere affects the electromagnetic radiation from the Sun that passes through it
- all objects emit electromagnetic radiation
- warm objects emit infrared radiation which you can see with a thermal imaging camera
- the type of radiation that an object emits depends on its temperature
- the hotter the object, the higher the frequency of radiation that it emits
If an object emits:
- the same amount of radiation as it absorbs, its temperature stays constant
- more radiation than it absorbs, its temperature decreases
- less radiation than it absorbs, its temperature increases
EARTH - TEMPERATURE
- Earth absorbs radiation from the sun
- Earth emits radiation into space
- Earth's atmosphere reflects some of the radiation back onto the earth
- Type and intensity of radiation reflected back to Earth depends on the concentration of greenhouse gases in the atmosphere
- The increasing concentration of greenhouse gases in the atmosphere means that the Earth's temperature is increasing
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Outline the process between radiation and the Earth's atmosphere
1) The Earth receives electromagnetic radiation from the Sun, including infrared, visible light and ultraviolet radiation
2) Some of the Sun's radiation is:
- absorbed by the atmosphere
- reflected back into space
3) The Earth's surface radiates infrared back into space because it is warmed by the Sun
4) Some of the Earth's infrared is reflected back towards the Earth's surface by the atmosphere
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What direction does radiation intensity go from?
Low to high radiation intensity
| High to low frequency
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Describe the Earth's structure
- centre of earth is about 6370km below the earth's surface
- has a solid inner core
- has a liquid outer core
- the mantle is almost entirely solid but it can flow
- the crust (which we live on) is solid
- deepest hole drilled by engineers was 12km long (they found that it got much hotter as they went down)
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How can the differences in velocity, absorption and reflection between different types of waves in solids and liquids be used for detection and for exploration of structures which are hidden from direct observation, notably in the Earth's core and in deep water?
- Earthquakes produce waves called seismic waves
- Scientists have used seismometers since the 1850s to detect seismic waves
- seismometers can detect seismic waves near the earthquake centre - there are seismometers all over the world (however, there are shadow zones where you cannot detect either/neither seismic waves)
- shadow zones = because S-waves cannot travel through liquid core so they are not detected on the other side of the Earth & produced by refraction of P waves
- A seismogram records the arrival and intensity of two types of seismic waves (P &S)
P WAVE
- primary waves
- can travel through earth
- longitudinal (so can travel through solids and liquids - like sound waves)
- Lehmann discovered that inner core (very centre of earth) is solid
S WAVE
- secondary wave
- cannot travel through earth
- transverse waves (so cannot travel through liquid)
- therefore, the core of the earth is liquid
SONAR
- used by submarines and fishermen to find distances using the time for an echo and the speed of sound in water
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Who answered the question as to why P-waves can travel through the Earth but S-waves cannot?
Bruno Gutenberg
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Practical Activity Group 4: Measure the speed of sound.
1) Connect two microphones to an oscilloscope
2) Place them about 2 m apart using a tape measure to measure the distance between them
3) Set up the oscilloscope so that it triggers when the first microphone detects a sound, and adjust the time base so that the sound arriving at both microphones can be seen on the screen
4) Make a large clap using the two wooden blocks next to the first microphone
5) Use the oscilloscope to determine the time at which the clap reaches each microphone and the time difference between them
6) Repeat this experiment for several distances, e.g. 2 m, 2.5 m, 3 m, 3.5m etc
PRECAUTIONS
1) Ensure to take repeat readings when timing intervals and calculate an average to keep this error to a minimum
2) Maximise the distance between the two people where possible
BECAUSE
this will reduce the error in measurements of time because the time taken by the sound waves to travel will be greater
CLAP-ECHO METHOD
- measuring the time taken for you to hear an echo from a sharp clap.
1) You stand a long distance from a wall, clap, and listen for the echo. The distance travelled is twice the distance from you to the wall (because the sound has to travel to the wall and back).
2) measure the time for 11 claps, which is the time for 10 journeys by the sound.
3) This time can then be used to calculate an average time for the sound to travel to the wall and back.
PRECAUTIONS
clap in time to the echoes. This means that the time between each clap is the journey time for the sound.
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Practical Activity Group 8: Investigate light waves reflecting, refracting and being absorbed.
1) Set up a ray box, slit and lens so that a narrow ray of light is produced.
2) Place a 30 centimetre (cm) ruler near the middle of a piece of plain A3 paper. Draw a straight line parallel to its longer sides. Use a protractor to draw a second line at right angles to this line. Label this line with an 'N' for 'normal'.
3) Place a plane mirror against the first line.
4) Use the ray box to shine a ray of light at the point where the normal meets the mirror. This is the incident ray.
5) The angle between the normal and the incident ray is called the angle of incidence. Move the ray box or paper to change the angle of incidence. The aim is to see a clear ray reflected from the surface of the mirror.
6) Using a pencil on the paper, mark the path of the incident ray with a cross & the reflected ray with a cross
7) Remove the mirror. Join the crosses to show the paths of the light rays.
8) Measure the angle of incidence and angle of reflection for the mirror.
9) Repeat steps 2 - 8 for several different angles of incidence.
ANALYSIS
Compare the angle of incidence with the angle of reflection for each block.
EVALUATION
The light rays should obey the law of reflection (In reflection at a surface, the angle of incidence equals the angle of reflection) for every attempt.
To what extent do the results show this?
PRECAUTIONS
1) Do not touch bulb and allow time to cool
BECAUSE
the ray box will get hot which may lead to minor burns
2) Ensure environment is clear of potential trip hazards before lowering lights
BECAUSE
the experiment is conducted in a semi-dark environment which increases the trip hazard
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Practical Activity Group 5: Investigate work done and measure the specific heat capacity of a metal.
1) Place the immersion heater into the central hole at the top of the block.
2) Place the thermometer into the smaller hole and put a couple of drops of oil into the hole to make sure the thermometer is surrounded by hot material.
3) Fully insulate the block by wrapping it loosely with cotton wool.
4) Record the temperature of the block.
5) Connect the heater to the power supply and turn it off after ten minutes.
6) After ten minutes the temperature will still rise even though the heater has been turned off and then it will begin to cool. Record the highest temperature that it reaches and calculate the temperature rise during the experiment.
energy transferred = potential difference × current × time
EVALUATION
- not all of the heat from the immersion heater will be heating up the aluminium block, some will be lost to the surroundings
- More energy has been transferred than is needed for the block alone as some is transferred to the surroundings. This causes the calculated specific heat capacity to be higher than for 1 kg of aluminium alone
PRECAUTIONS
- Do not touch when switched on.
- Position away from the edge of the desk.
- Allow time to cool before packing away equipment.
- Run any burn under cold running water for at least 10 minutes.
OTHERWISE
Hot immersion heater and sample material may lead to burnt skin
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focal length
focal length = the distance from the optical centre of the lens to the focal point, when the rays going into the lens are parallel
