Physics Flashcards
1
Q
What is chemical energy?
A
Energy which is obtained from fuels, foods, and chemicals in batteries.
2
Q
What is kinetic energy?
A
Energy in a moving object.
3
Q
What is gravitational potential energy?
A
The potential energy of an object due to it being above the ground.
(Usually transfers into kinetic energy.)
4
Q
What is elastic potential energy?
A
The potential energy when an object is stretched or squashed.
5
Q
What is thermal energy?
A
Energy in an object due to its temperature.
6
Q
What is the principle of conservation of energy?
A
Energy cannot be created or destroyed.
7
Q
What is a closed system?
A
An object or group of objects where no energy transfer takes place into or out of the system.
8
Q
What is useful energy?
A
Energy which is transferred to where it is wanted in the form it is wanted in.
9
Q
What is wasted energy?
A
Energy which is not usefully transferred.
10
Q
What is energy dissipation?
A
When energy is transferred into the surroundings.
11
Q
What is efficiency?
(In terms of energy.)
A
How much energy is usefully transferred, usually expressed as a percentage.
12
Q
How can machines be made more efficient?
A
- Lubricants to reduce friction.
- Streamlining to reduce air resistance.
- Copper wires to minimize electrical resistance.
13
Q
How is energy usefully transferred by:
1) A light bulb
2) An electric mixer
3) A speaker
4) A television
A
1) Light waves emitted from the filament.
2) Work done by blades of mixer.
3) Sound waves from vibrations of speaker cone.
4) Light waves and sound waves.
14
Q
What is power?
(In terms of energy.)
A
The rate at which an appliance transferrs energy.
15
Q
What is the unit of power?
A
Watts (W)
16
Q
What is efficiency?
(In terms of power.)
A
How much power is usefully outputted.
17
Q
What is a thermal conductor?
A
A material that allows thermal energy (heat) to move through them easily.
For example, metals.
18
Q
What 3 factors affect the rate of thermal energy transfer through a material?
A
1) Temperature difference across the metal.
2) Thickness of the material.
3) Thermal conductivity of the metal.
19
Q
Why do saucepans often have wooden handles?
A
Wood is a poor thermal conductor, meaning that heat from the pan won’t reach the handle.
20
Q
Why do materials that trap air have low thermal conductivities?
A
Air is a good insulator of thermal energy, meaning that heat won’t pass through easily.
21
Q
What is a specific heat capacity?
A
The amount of energy required to raise the temperature of 1kg of substance by 1°C.
22
Q
Name 5 ways buildings can be insulated / heated.
(Or name as many as you can.)
A
1) Fibreglass loft insulation. Reduces rate of energy transfer through the roof.
2) Cavity wall insulation. Reduces rate of energy transfer through the walls.
3) Aluminium foil behind radiatiors. Reflects infrared radiation back into the room.
4) Double glazing windows. Reduces rate of energy transfer through the windows.
5) Thick bricks with low thermal conductivity. Reduces rate of energy transfer through outer walls.
23
Q
How do solar panels work?
A
They absorb infrared radiation (energy) from the sun and make energy directly through this. Some solar panels however, will use the energy to heat water to create thermal energy.
24
Q
Name 3 fossil fuels.
A
- Oil
- Gas
- Coal
25
Name 2 non-renewable energy sources.
- Fossil fuel
- Nuclear fuel
26
Name 6 renewable energy sources.
(Or as many as you can)
- Biofuel
- Wind energy
- Hydroelectricity
- Geothermal energy
- Solar energy
- Wave energy
27
How is nuclear fuel created?
When the unstable nucleus of a uranium atom splits in two, which releases energy.
28
What are the advantages and disadvantages of nuclear power?
**Advantages**
- They do not produce greenhouse gases.
- Nuclear fuel produces more energy per kilogram than fossil fuels.
**Disadvantages**
- Production of nuclear waste such as fuel rods which need to be stored safely for centuries.
- An accident can make the surrounding area unsafe for years.
29
What are the advantages and disadvantages of renewable energy sources?
**Advantages**
- They will not run out and are produced fast.
- They do not produce dangerous waste.
- Mostly do not contribute to climate change.
**Disadvantages**
- Cannot meet the current demand for energy.
- Some sources are not available all the time.
- Some people may think that structures for these energy sources are unsightly and they can affect animal / plant life.
30
What is static electricity?
When two electrically insulating materials are rubbed together, causing electrons to transfer from one object to the other.
| (Direction of electron transfer depends on the materials.)
31
What does a charged object have around itself?
An electric field.
32
When are 2 objects repelled?
When they have the same electric charge.
33
When are 2 objects attracted?
When they have opposite charges.
34
What is a charge carried by?
Electrons.
35
What is the unit of charge?
Coulombs (C)
36
What does a diode do?
Allows current to flow in only one direction.
37
What does a cell (or battery) do?
Pushes electrons around a complete circuit.
38
What does a switch do when it is:
1) Open
2) Closed
1) Doesn’t allow current to flow.
2) Allows current to flow.
39
What does a bulb do?
Emits light as a signal when a current passes through it.
40
What does a light-emitting diode (LED) do?
Emits a light when a current passes through.
| (Current can only flow in one direction through an LED.)
41
What does an ammeter do?
Measures the current in a circuit.
| (Connected in series with the circuit.)
42
What does a fixed resistor do?
Limits the current at a fixed value.
43
What does a variable resistor do?
Allows the resistance, and therefore the current, to be varied.
44
What does a fuse do?
Designed to melt if the current is greater than a certain amount and therefore breaking the circuit.
45
What does a heater do?
| (In a circuit.)
Transfers energy from an electric current to heat the surroundings.
46
What does a voltmeter do?
Measures potential difference (voltage) in a circuit.
| (Connected in parallel.)
47
What is resistance?
| (In a circuit)
Opposition to current flow.
48
What is Ohm's Law?
When a resistor's current is directly proportional to its potential difference.
49
What is an ohmic conductor?
A component which follows Ohm's law.
50
What does a thermistor do?
Decreases resistance as temperature increases and vice versa.
51
What does a light-dependent resistor (LDR) do?
Decreases resistance as light shining upon it gets brighter and vice versa.
52
What is a series circuit?
A circuit where all components are connected one after the other.
| (If there is a break anywhere, the whole circuit will break.)
53
What is a parallel circuit?
A circuit with 2 or more branches.
| (If a component on one branch breaks, other branches will still work.)
54
How do you calculate the current of a circuit with multiple branches?
Add the current of all branches together.
55
How do you calculate total resistance in a series circuit?
Add the resistance of all components.
56
How do you calculate resistance in a parallel circuit?
**Add the resistance of the reciprocal of all components in the branches. Then, reciprocate the answer to get the resistance.**
*For example, branches with a resistance of 2Ω, 5Ω and 10Ω would be converted into 5/10, 2/10 and 1/10 (with common demominators in the fraction.) These fractions would be added together which would be 5/10 + 2/10 + 1/10 = 8/10. The answer is the reciprocated, meaning the resistance of the parallel circuit is 10/8, which is 1.25 Ω.*
57
What is a direct current?
A current that passes round a circuit in one direction.
58
What is an alternating current?
A current which repeatedly changes direction.
59
What is the frequency of the UK's mains supply? And what does this mean?
50 hertz (Hz). This means that the mains current revereses its direction 50 times per second.
60
What colour is the live wire and what does it do?
It is brown and it alternates between positive and negative voltage.
61
What is the peak voltages of the live wire?
+325V to -325V
62
What colour is the neutral wire and what does it do?
It is blue and it completes the circuit back to the power supply.
63
What colour is the earth wire and what does it do?
It is striped green and yellow and it provides a path into the earth to avoid electric shocks.
64
What is the National Grid?
A system of cables and transformers which link stations to consumers.
65
What are step-up and step-down transformers?
A step-up transformer increases voltage from the station to the transmission cables. A step-down transformer decreases voltage for domestic use.
66
What is the potential of the neutral wire?
0 Volts (V)
67
What is the outer layer of a plug made of and why?
It is made of a stiff plastic material because it is a good insulator.
68
What are the pins of the plug made of and why?
They are made of brass because it is a good electrical conductor and it doesn't rust/oxidise.
69
What is the longest pin in a plug and why?
The earth wire so that it connects to the socket first.
70
Why do plugs contain fuses?
So that if the current gets too high, the circuit will be disrupted and stopped.
71
What is the voltage of the mains supply?
230 Volts (V)
72
Why should the fuse current rating be slightly higher than the current through the appliance?
So that the fuse will melt only if the expected current is exceeded.
73
What is density?
Measurement of mass per unit volume, usually measured in kg/m³
74
What is the alternative measurement to kg/m³ and its conversion?
g/cm³.
1000kg/m³ = 1g/cm³
75
Order the 3 states of matter from most to least energetic.
1) Gas
2) Liquid
3) Solid
76
What is latent heat?
Energy transferred to or from a substance as it changes states.
77
What is internal energy?
The total energy in the kinetic energy and potential energy store in a substance.
78
What happens to particles when temperature increases?
Kinetic energy increases.
| (i.e. they move around faster.)
79
What are the forces of attraction like in the 3 states of matter?
Solid: strong forces
Liquid: weak forces
Gas: negligible forces (too small to be noticed.)
80
How is pressure created?
When gas particles collide with each other and the walls of a container. These collisions exert a force.
81
What is the specific latent heat of fusion?
Energy needed to change 1kg of substance from solid to a liquid.
82
What is the specific latent heat of vaporisation.
The energy needed to change 1kg of substance from liquid to vapour.
83
What happens to pressure if a fixed mass of gass has:
1) Less space
2) More space
1) Pressure will increase.
2) Pressure will decrease.
84
What is the relationship between pressure and volume?
They are inversely proportional.
85
Why are some substances radioactive?
They have unstable nuclei, they become stable by radioactive decay where they emit radiation.
86
What are the 3 types of nuclear radiation?
1) Alpha
2) Beta
3) Gamma
87
Can rate of decay of a radiocative substance be changed manually?
No, it is a random process and no external conditions can affect the rate of decay.
88
If most alpha particles passed through the gold foil, what does this mean for the atom?
Most of the atom is empty space.
89
What does an alpha particle consist of?
2 protons and 2 neutrons.
Mass number = 4
Atomic number = 2
Charge = +2
90
What does a beta particle consist of?
1 electron.
Mass number = 0
Atomic number = -1
Charge = -1
91
What does gamma radiation consist of?
An electromagnetic wave released from the nucleus.
Mass number = 0
Atomic number = 0
Charge = 0
92
What is ionisation?
When electrons are lost or gained.
93
What is radioactive contamination?
When there are unwanted materials with radioactive atoms on other materials.
94
What are the ionising powers of the 3 nuclear radiation types?
Alpha - Strongly ionising
Beta - Moderately ionising
Gamma - Weakly ionising
95
What are the relative masses of the 3 nuclear radiation types?
Alpha: 4u (large)
Beta: 1/1845u
Gamma: 0u
96
What are the penetrating powers of the 3 nuclear radiation types?
Alpha - Weak penetration
Beta - Moderate penetration
Gamma - High penetration
97
What are the ranges in air of the 3 nuclear radiation types?
Alpha: 5cm
Beta: 1m
Gamma: Unlimited
98
What are the 3 types of nuclear radiation absorbed by?
Alpha: Thin sheet of paper or skin.
Beta: 5mm thick aluminium sheet or 2-3mm thick lead sheet.
Gamma: Thick lead sheet.
99
Where are the 3 types of nuclear radiation deflected to in an electric field?
Alpha: Towards negative plate.
Beta: Towards positive plate.
Gamma: No deflection.
100
What is 'activity' of a radioactive source?
Number of unstable atoms in the source which decay per second.
| (This is also the count rate.)
101
What is half-life?
- Average time it takes for the number of nuclei to halve
- Average time it takes for count rate to halve
102
What is radioactive activity measured in?
Becquerel (Bq)
103
What is a radioactive tracer and how do they work?
A machine used to measure the flow of a substance through an object. The patient drinks or is injected with a radioactive isotope which emits gamma radiation. The gamma radiation is then monitored through a gamma detector.
104
Why is gamma radiation usually used for medicine instead of other types of nuclear radiation?
It can penetrate through skin and go deep into the body.
105
Why do medical tracers have half-lives of just a few hours?
The half-life is long enough to complete imaging but short enough to not expose the patient to unneccessary radiation.
106
What is nuclear fission?
The splitting of an atomic nucleus into 2 smaller nuclei.
107
What does nuclear fission release?
- 2 or 3 high speed neutrons.
- Energy in the form of gamma radiation and kinetic energy of the nuclei and neutrons.
108
Which 2 isotopes are involved in nuclear fission?
- Uranium-235
- Plutonium-239
109
What is induced fission and spontaneous fission?
Induced fission is when a neutron is absorbed into the nucleus and causes fission.
Spontaneous fission is when fission occurs without a neutron being absorbed, however this is rare.
110
What is a chain reaction in nuclear fission?
When neutrons released from previous fission causes more fission events to occur.
111
How is nuclear fission controlled in a nuclear reactor?
Control rods in the reactor core are used to absorb surplus neutrons. The height of the rods are adjusted to maintain a steady chain reaction.
112
What is nuclear fusion?
When 2 nuclei are close enough together to form a larger nucleus.
113
What process releases energy in the Sun?
Nuclear fusion.
114
How are nuclei contained in a fusion reactor?
Using a magnetic field.
115
What are the 2 major sources of background radiation for a person in the UK.
Radon gas and cosmic rays.
116
Why must radioactive waste be stored safely?
It emits radiation which can cause cancer and have other harmful effects.
117
What is a vector quantity?
A measurement of both magnitude and direction.
118
What is a scalar quantity?
A measurement of magnitude but no direction.
119
What is displacement?
Distance in a certain direction.
120
What is a force?
A push or pull action on an object due to an interaction with another object.
121
What is Newton's third law of motion?
When 2 objects interact with each other, they exert equal and opposite forces on each other.
122
What is the unit of force?
Newtons (N)
123
In what way does weight force always act?
Downwards
124
What is a resultant force?
The overall magnitude and direction of 2 or more forces.
125
What is Newton's first law of motion?
If the forces acting on an object are balanced, the resultant force is 0. Also, if an object is at rest, it will stay at rest. If an object is moving, it will maintain the same speed.
126
What is a moment?
The turning effect of a force.
127
What are moments measured in?
Newton metres (N m)
128
Which 2 ways can increase a moment?
- Increasing the magnitude of the force.
- Increasing perpendicular distance from the line of force to the pivot.
129
What are the differences between a low and high gear?
**Low:** Low speed, high turning effect.
**High:** High speed, low turning effect.
130
What is the centre of mass?
The point at which it is thought that all mass is concentrated in an object.
131
What is the principle of moments?
If an object isn't turning, it is at equilibrium. Both clockwise and anticlockwise moments are equal.
132
What is the method used to find the magnitude and direction of 2 different forces?
Drawing a parallelogram proportionally with both forces.
133
What does gradient on a distance-time graph represent?
Speed
134
What is velocity?
Speed in a given direction.
135
What does the gradient on a velocity-time graph represent?
Acceleration
136
What does it mean if the gradient on a velocity-time graph is negative?
The object is decelerating.
137
What does the area under a velocity-time graph represent?
Distance travelled in a given direction.
138
How can you find the gradient on a curved line?
Drawing a tangent at a given point and calculating the gradient of the tangent.
139
What is Newton's second law of motion?
The acceleration of an object is proportional to the resultant force.
The acceleration of an object is also inversely proportional to the mass.
140
What is inertia?
The tendancy for an object to stay at rest or at a constant speed in a straight line.
141
What is the drag force when an object is falling out of the sky?
Air resistance
142
What is stopping distance?
The distance a vehicle travels from reaction of the driver to being stationary.
(Stopping distance = thinking distance + braking distance)
143
What is the law of conservation of momentum?
Whenever objects interact in a closed system, the amount of momentum before the interaction is equal to the total momentum after the interaction.
144
What happens when 2 vehicles collide in terms of momentum?
- Exert equal, but opposite forces on each other.
- Change in momentum of one vehicle is equal and opposite to the change in momentum of the other vehicle.
- Therefore, total momentum remains unchanged.
145
What are the safety features on a modern car?
- Seat belts
- Airbags
- Crumple zones
- Side impact bars
146
What is an elastic object?
An object which regains its original shape when the forces deforming it are removed.
147
What is the extension of a spring?
The increase in a spring's length from the original length.
148
What is the relation between extension and force applied?
They are directly proportional.
149
What is the limit of proportionality for a spring?
When too big of a force is applied on a spring, the graph will no longer be directly proportional.
150
What is pressure measured in?
Pascals (Pa)
or
N/m²
151
How would pressure differ in different areas in a body of water?
- Further down a liquid has a greater pressure because there is more water above pushing down.
- A greater density of water has a greater pressure.
152
How is atmospheric pressure created?
Air molecules in the Earth's atmosphere collide with surfaces. Every impact creates a small force on the surface.
153
How does atmospheric pressure change with altitude?
The lower you are, the more pressure. This is because the air is more dense and there is a greater weight of air above you.
154
What is upthrust?
The upward force when the an object's resultant force upwards is greater than the resultant force downwards when it is underwater. This will result in the object being pushed upwards.
155
What is the upthrust force equal to?
The amount of water being displaced.
156
How does density affect if an object will sink in water or not?
An object with a density greater than the water it is immersed in will sink.
An object with a density less than the water it is immersed in will float.
157
What is a transverse wave?
A wave where the particles oscillate perpendicular to the direction of energy transfer (i.e. perpendicular to the direction the wave is travelling in.)
158
What is a longitudinal wave?
A wave where the particles oscillate parallel to the direction of energy transfer (i.e. parallel to the direction the wave is travelling in.)
159
What is a mechanical wave?
A wave which travels through a medium (a material.)
160
What is an electromagnetic wave?
A wave that travels through a vacuum (or space)
161
What is the amplitude of a wave?
The maximum height or depth of a wave from the midpoint.
162
What is the wavelength of a transverse wave?
Distance from one point in an oscillation to the same point in the next oscillation in a wave.
163
What is the frequency of a transverse wave?
The number of wave crests passing through a point every second, measured in hertz (Hz.)
164
What is the period of a wave?
Time taken for one wavelength to pass a point.
165
What is the wavelength of a longitudinal wave?
Distance from the middle of one compression the the middle of the next compression.
166
What is the frequency of a longitudinal wave?
Number of compressions passing through a point in one second.
167
What 3 things could happen when a wave meets a boundary?
- Be totally or partially reflected by the boundary
- Transmit through the boundary
- Be absorbed by the boundary
168
How are echoes created?
When sound waves reflect off surfaces.
169
What does change in frequency do to a sound wave?
Higher frequency = higher pitch
Lower frequency = lower pitch
170
What does change in amplitude do to a sound wave?
Greater amplitude = louder sound
Smaller amplitude = quieter sound
171
How do ultrasound scanners work?
A device called a **transducer** produces an ultrasound wave. When the wave meets a boundary between 2 different materials, the wave is **partially reflected**. The wave travels back through the material to be **detected by the transducer**. The time taken for the wave to return can be used to calculate how far away the boundary is. Results are processed by a computer to create an image.
172
What is the 'focus' of an earthquake?
The point at which an earthquake originates from.
173
What is the 'epicentre' of an earthquake?
The closest point on the Earth's surface to the focus of the earthquake.
174
What are the 4 layers of Earth?
| (Order from outermost to innermost layer)
1) Crust
2) Mantle
3) Outer core
4) Inner core
175
What does a seismometer do?
Detects movements in the Earth's crust causes by seismic waves.
176
What are the characteristics of seismic p-waves?
- Primary seismic waves
- Longitudinal waves
- Quicker than s-waves
- Refract at the boundary between the mantle and the core.
- Speed up as depth increases (greater density lower down)
177
What are the characteristics of seismic s-waves?
- Secondary seismic waves
- Transverse waves
- Slower than p-waves
- Bend as they travel from the focus to the mantle.
- Cannot travel through outer core (cannot travel through liquids)
178
What is a shadow zone?
Areas where either p-waves or s-waves don't reach because they are refracted or absorbed.
179
List all electromagnetic waves from longest wavelength to shortest wavelength
- Radio waves *(longest)*
- Microwaves
- Infrared
- Visible light
- Ultraviolet
- X-rays
- Gamma rays *(shortest)*
180
What speed do electromagnetic waves travel at?
300 million m/s (speed of light)
181
How are colours that compose white light different from each other?
Different wavelengths
| (Red is the longest and violet is the shortest.)
182
What is infrared radiation emitted by?
All objects
183
Which type of substances absorb and emit the most infrared?
Darker substances
Hotter substances also emit more infrared
184
What are carrier waves?
Waves used to carry any type of signal
185
What are the characteristics of short and long wavelengths when it comes to carrying information?
**Shorter**
- Carry more information
- Shorter range
- Less spread out
**Longer**
- Carry less information
- Longer range
- More spread out
186
How can ultraviolet be dangerous?
- Can cause sunburn
- Can cause skin cancer
- Can harm eyes
187
How do x-rays work medically?
They pass through soft tissues and skin, but are absorbed by bones, teeth and metal objects that aren't too thin. Therefore, they can be used to check for fractures and dental problems.
188
What is the 'normal'?
| (To do with light rays)
A line perpendicular to the mirror where the incident ray hits the mirror.
189
What is the angle of incidence?
The angle between the incidence ray and the normal
190
What is the angle of reflection?
The angle between the reflected ray and the normal
191
What is the correlation between the incidence ray and the reflected ray?
| (On a flat surface)
They are always equal
192
What is diffuse reflection?
Reflection from a rough surface, incident rays are reflected in different directions.
193
What is refraction?
When any kind of wave changes direction as it changes speed at a boundary
194
What is the angle of refraction?
The angle between the refracted ray and the normal
195
What happens when light hits a:
1) Transparent object
2) Translucent object
3) Opaque object
**Transparent:** all light is transmitted.
**Translucent:** some light passes through, some is absorbed. The light that passes through is scattered or refracted.
**Opaque:** all light is absorbed
196
What happens when light hits:
1) A white surface
2) A black surface
3) A coloured surface
**White:** all light is reflected
**Black:** all light is absorbed
**Coloured:** the colours in the visible light spectrum that make the colour of the surface are reflected. The rest are absorbed.
197
What is a zero error?
When a measuring instrument gives a false reading when the true value is actually zero
198
What is a random error?
When ther is an unpredictable variation due to things you have no control over
199
What is a systematic error?
When the measuring instrument reads a value which differs from the real value by a consistent amount each time the measurement is made
200
What is the gravitational field strength of earth?
9.8N/kg
201
Which factors can affect thinking distance?
- Alcohol or drug influence
- Caffeine
- Distractions
- Tiredness
- Using a mobile phone
202
Which factors can affect braking distance?
- Road conditions
- Brake conditions
- Tyre conditions
- Poor weather
203
How is impact force decreased?
- Increase stopping time
- Decrease rate of momentum change
- Decreases force
204
How is impact force increased?
- Decrease stopping time
- Increase rate of momentum change
- Increases force
205
What does a concave lens do?
Causes light that passes through to diverge
206
What does a convex lens do?
Causes light that passes through to converge
207
What is a magnetic field?
A region around a magnet where a magnetic material experiences a force
208
What is a solenoid?
A wire which is coiled up into a spiral, the wire can create a magnetic field when a current flows through
209
How can a magnetic field around a wire be strengthened?
- Greater current
- More coils
- Add a core
210
What does each finger refer to in Fleming's Left Hand Rule?
**Thumb** - direction of force
**Index** - direction of magnetic field
**Middle** - direction of current
211
What is a split ring commutator?
A device which allows the current around a coil to reverse every half turn in the motor effect
212
How can size of an induced current (or p.d) be increased?
- Moving wire up and down more quickly
- Using a stronger magnetic field
- Greater number of coils
213
How can direction be changed in the motor effect?
- Alternating current
- Split ring commutator
214
What makes a transformer?
- Primary coil
- Secondary coil
- Iron core
215
What is the difference between a step-up transformer and a step-down transformer?
A **step-up transformer** has less turns on the primary coil than the secondary coil
A **step-down transformer** has more turns on the primary coil than the secondary coil
216
What is a dynamo?
A direct-current generator which uses a split-ring commutator
217
What are the stages in the formation of a star?
- Gravity pulls a **nebula** (cloud of gas) inwards. Increased density results in increased temperature and pressure inside.
- A **protostar** is formed as gravity pulls gases into a ball. Temperature continues to increase.
- At the high temperature, hydrogen fuses through nuclear fusion which radiates energy (radiation pressure.)
- The star is stable because the inward force of gravity and the outward force of radiation pressure are balanced, creating a **main sequence star**.
218
What are the conditions needed for nuclear fusion?
- High temperature
- High pressure
- High kinetic energy in nuclei
219
What are the stages in the death of a star?
- Star begins to run out of hydrogen for nuclear fusion. This stops the radiation pressure.
- The star expands and becomes a expands and becomes a giant and cools, making it appear red. It is now a **red giant**.
- Red giants are unstable so heat and pressure from its core ejects the outer layers of the star into space. The outer layers are called **planetary nebula**.
- The exposed core following the formation of a planetary nebula is known as a **white dwarf**.
- White dwarfs slowly cool until giving off no light, which creates a **black dwarf**.
220
What are the stages in the death of a massive star?
- Star runs out of hydrogen for nuclear fusion. This stops radiation pressure.
- Star expands into a supergiant and cools, so appears red. This is called a **red supergiant**.
- Core contracts further and allows carbon to fuse. This produces heavier elements which also fuse until iron is formed, which cannot fuse, so fusion stops abruptly.
- Gravity pushes into the core, and the star suddenly collapses and implodes. Implosion bounces of the core, creating an enormous shockwave. The massive release of energy is called a **supernova**, and leaves behind the core.
- Supernovae are powerful, so create new atomic nuclei. The shockwave slams nuclei into one another with such force that it can create nuclei heavier than iron. This is **nucleosynthesis**.
- The core collapses, crushing protons and electrons, forming neutrons. This leaves behind a **neutron star**. *Or*, the core is large enough with gravity so strong that no force can stop its collapse. This forms a **black hole**.
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What is an orbit?
A curved path of an object around another object, typically a planet or a star.
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What is a centripetal force?
The force needed for an object to continue moving in a circle
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Why might a galaxy appear blue?
Blue light has shorter wavelengths. These shorter wavelengths are from the relative movement of the galaxy with the waves when galaxies move towards us. So galaxies appear blue due to a blue shift.
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Why might a galaxy appear red?
Red light has longer wavelengths. These longer wavelengths are from the relative movement of the galaxy with the waves when galaxies move away from us. So galaxies appear red due to red shift.
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What is the Steady State Theory?
The universe has always existed and is expanding and creating matter while doing so. Density of the universe remains the same as it expands.
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What is the Big Bang Theory?
Our universe started in a very hot and very dense state. Then nearly 14 billion years ago, expansion started. The universe stretches and density changes hugely over time.
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What is CMBR?
**Cosmic Microwave Background Radiation**
Initially created as high energy gamma radiation just after the Big Bang. As the universe expanded, the wavelengths got longer, and is now microwave radiation.
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Why is the Big Bang Theory accepted ahead of the Steady State Theory?
The Big Bang Theory can explain red shift and CMBR, whereas the Steady State Theory can only explain red shift.
