# P2

What is the velocity of an object?
Its speed in a given direction, if its direction it changes velocity even if the speed stays the same. Increase in velocity = acceleration. Negative acceleration = deceleration (object is slowing down).
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What can a velocity-time graph show?
Acceleration given by gradient. Distance travelled shown by calculating area of shape beneath gradient. If line=horizontal, acceleration=0 + object is moving at a steady pace. Negative gradient = deceleration.
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What can a distance-time graph show?
Speed given by gradient. The steeper the grad, the greater the speed. Constant speed = straight line that slopes upwards. Stationary = horizontal line.
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What are action and reaction forces and how can they be applied?
Objects always exert equal and opposite forces on each other. i.e is a car is being driven forwards, there is a force from the tyre on the ground pushing backwards. If you place a book on the table, the table will exert eq+opp forces upwards on the b
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What is resultant force and what happens when the resultant force is zero?
The single force that would have the same effect on the object as all of the original forces acting together. When at zero: if the objects at rest, it will stay at rest or if the object is moving, it will carry on moving at the same speed + direction
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What does it mean when the resultant force of an object is not at zero?
There will be an acceleration in the direction of the force. A resultant force always causes an acceleration and is needed to make an object change direction. The greater the resultant force on an object, the greater its acceleration
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What does it mean when the resultant force is not at zero?
If object is at rest, it will accelerate in direction of resultant force, if moving in the same direction as resultant force it will accelerate in that direction. If moving in opposite direction to the resultant force it will decelerate.
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What affects the braking force needed and what is the stopping distance?
The faster the speed of a vehicle, the bigger the deceleration needed to stop it in a particular distance = the bigger the braking force needed. Stopping distance = distance travelled: during drivers reaction time + travelled under the braking force
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What can affect the thinking + braking distance?
Reaction time is increased if the driver is tired or under the influence of alcohol/drugs. Braking distance affected by poorly maintained roads/adverse weather conditions + Condition of the car i.e. worn tyres/brakes will increase it.
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What is the resultant force acting on an object that fall freely?
Gravity (will make object falling near earth’s surface accelerate at 10m/s2). Force of gravity is called weight and the acceleration = acceleration due to gravity (W = m × g).
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What happens when an object falls through a fluid?
Fluid exerts a drag force on the object resisting its motion. Faster the object falls, bigger the drag force becomes until its equal to the weight of the object. Resultant force is now 0 so object stops accelerating + moves at terminal velocity (cons
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What is an elastic object?
One that regains its original shape when the forces deforming it are removed i.e. when weights are hung from a spring the increase in length from the original is called an extension.
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What do we obtain when we plot a graph of extension against force applied for a spring?
A straight line that passes through the origin which tells us that the extension is directly proportional to the force applied. If we apply too big a force the line begins to curve because we have exceeded the limit of proportionality.
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What does Hooke’s law state?
That the extension is directly proportional to the force applied provided the limit of proportionality isn’t exceeded. F = k × e
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What happens when a string is stretched (in terms of energy)?
When an elastic object is stretched, work is done and stored as EPE (elastic potential) in the object, when the stretching force is removed this stored energy is released. The stiffer a spring is, the greater its spring constant.
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What is fuel economy and how can we improve fuel economy?
Reducing the speed of a vehicle reduces the amount of fuel used. Reducing the air resistance by making the vehicle more streamlined (i.e. fitting a wind deflector) also improves fuel economy.
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Why are speed cameras used?
To discourage motorists from speeding as they can determine the speed of a motorist at a particular point. Motorists caught speeding are fined and may lose their license.
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When does skidding happen?
When the brakes on a vehicle are applied too harshly. When a vehicle skids, the wheels lock and slide along the road surface, increasing the stopping distance
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How can skidding be reduced?
By using anti-skid surfaces that are rougher than road surfaces, increasing the friction between the vehicle tyres and the road. They are used in places where drivers are likely to brake i.e. near traffic lights/road junctions.
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What happens when an object starts to move and what is the equation for work done?
A force has been applied to it – energy is transferred + work is done. When work is done moving the object, the supplied energy is transferred. If no work is don then the distance moved is 0. W (J) = Force (N) × distance moved in direction of the fo
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Which force is work done to overcome?
Friction-mainly transferred into energy by heating i.e. when brakes are applied in a car the friction between the wheel discs + brake pads oppose motion of the wheel. Kinetic energy->thermal energy
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What is gravitational potential energy and how can it be calculated?
Energy stored in an object because of its position in the Earth’s gravitational field. When object is moved vertically GPE = work done (by lifting force). Change in GPE (J) = mass (kg) × Gravitational field strength (N/kg) × change in Height (m)
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What is power and how can it be calculated?
Power = rate of energy transfer. P = E ÷ t. Power (W) = Energy (J) ÷ time (s)
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What does the kinetic energy of a moving object depend on and what is the equation for Kinetic energy?
Greater mass + faster the speed, the more kinetic energy the objects has. Ek = ½ × m × v2. Kinetic Energy (J) = ½ × Mass (kg) × speed (m/s)
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What is elastic potential energy + what makes an object elastic?
How energy transferred when work is done on an elastic object to stretch/squash it is stored.Objext = elastic: When it regains its shape after being stretched/squashed.
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How is momentum affected and how can it be calculated?
The greater the mass + velocity the greater the momentum. P = m × v. momentum (kgm/s) = mass (kg) × velocity (m/s)
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What is the law of conservation of momentum?
Whenever objects interact, the total momentum before the interaction is equal to the total momentum afterwards (provided no external forces act on them).
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Objects at rest are at zero momentum. Why is the total momentum after an explosion zero?
In an explosion the objects move apart with equal + opposite momentum. 1 momentum is positive & the other negative so total momentum is 0 after the explosion i.e. bullet = gun recoils.
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Why are side impact bars and crumple zones built into cars?
They fold up in a collision to increase the impact time and reduce the forces acting.
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Why are seat belts and air bags built into cars?
As they spread the forces on the body across a larger area so that when the drivers head hits the airbag it changes the momentum slowly and seatbelt increases the impact time reducing the force.
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What happens when two electrically insulating materials are rubbed together?
Electrons are rubbed off one material on deposited on the other. As electron have a negative charge the material that has gained electrons becomes negatively charged + the one that has lost electrons becomes positively charged.
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What happens if two negatively charged objects are brought close together?
Oppositely charged objects attract, same charged objects repel. The bigger distance between the objects, the weaker the force between them.
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How is current and potential difference measured?
Ammeters measure current (amps) + are always placed in series with the component. Voltmeters measure pd + are always placed in parallel with the component.
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What is resistance and what is ?
Opposition to current flow in ohms. R = V / I
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What is Ohms Law?
When the current is directly proportional to the voltage across a resistor. Any component that obeys this it is an Ohmic conductor.
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Describe the current potential graph for a filament light bulb.
Not directly proportional. The resistance of the filament increases as the current increases because the temperature also increases. Reversing the Pd makes no difference to the curve. Current is the rate of flow of charge.
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Describe the current potential graph for a diode.
It is not directly proportional. It only flows in one direction because there is a large resistance in the other direction so the current is zero.
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Describe the resistance of light dependent resistors and thermistors.
As the light falling on it gets brighter, the resistance of an LDR decreases. As the temperature goes up, the resistance of a thermistor foes down.
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Describe a series circuit.
Components are connected one after another, so if there’s a break anywhere in the circuit the charge stops flowing. The current is the same in each component as there is no choice of route for the charge.
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How could you find the potential differences and resistances of the components?
Supply of pd shared between components. Resistances of the components add up to give the total resistance of the circuit. The bigger the resistance of a component, the bigger its share of pd.
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Describe a parallel circuit.
Each component is connected across the supply, so it there is a break in one part of the circuit, charge can still flow in the other parts.
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Describe the share of current and potential differences in parallel circuits.
As there are junctions in the circuit, different amounts of charge can flow through different components. The bigger the resistance, the bigger the smaller the current through it. Pd across each component is the same.
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What is direct current and alternating current?
D.C. – Cells/batteries supply current that passes round the circuit in one direction. A.C. – the current form the mains supply passes in one direction, then reverses and passes in the other direction.
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Describe the mains supply
The frequency of the UK mains supply is 50 Hertz (Hz) which means it changed direction 50 times per second. Mains voltage is 230 V.
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Describe the live wire of the mains supply.
The live wire of the mains alternates between a positive potential (peak voltage of +325V) & a negative potential (peak voltage of -325V) with respect to the neutral wire which stays at 0 volts.
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Why are certain parts of plugs made out of certain materials?
Outer cover made of plastic/rubber (good electrical insulator). Pins made of brass (good electrical conductor, hard, resistant to corrosion).
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Why don’t appliances with a plastic case need to be earthed?
Appliances with plastic cases do not need to be earthed as they are ‘double insulated’ + connected to 2-core cable containing only a live + neutral wire. Plastic is an insulator and cannot become live.
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Why do appliances with a metal cases need to be earthed?
As if a fault develops + the live wire touches the metal case, the case becomes live and could give a shock to anyone who touches it.
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What is the purpose of a fuse and how does it work?
Always fitted in series with the live wire and cuts appliance off from the from the live wire if the fuse blows.If a fault develops in an earthed appliance, a large current flows to earth and melts the fuse, disconnecting the supply.
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What does the rating of a fuse depend on?
The rating of a fuse should be slightly higher than the normal working current of the appliance. If its much higher it won’t melt soon enough, if it isn’t higher.
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What does the rating of a fuse depend on?
The rating of a fuse should be slightly higher than the normal working current of the appliance. If its much higher it won’t melt soon enough, if it isn’t higher then it will melt too soon.
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What is the difference between a circuit breaker and RCCB (Residual Current breaker)?
A circuit breaker is an electromagnetic fuse that opens and cuts of the supply if the current is bigger than a certain value whereas an RCCB cuts off the current in the live wire is it is different to the current in the neutral wire (faster).
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What is power?
The rate at which an electrical appliance transfers energy into other forms of energy.
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What should be taken into account when using and buying electrical appliances?
Avoid overloading sockets as they may cause overheating and a risk of fire and never use in a bathroom/with wet hands. Cost effectiveness i.e. Filament/halogen light bulbs are less efficient than low-energy light bulbs + don’t last as long.
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What is the basic structure of an atom?
A small central nucleus, made up of protons and neutrons, surrounded by electrons.
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How do the nuclei of radioactive substances become stable and list the three different types of radiation emitted as a result?
As the nuclei of radioactive substances are unstable, they become stable by radioactive decay emitting either alpha, beta or gamma radiation to turn into other elements. This is random + unaffected by external factors.
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Radiation that is around us all the time from radioactive substances in the environment, space + devices (i.e. X-ray tubes).
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What was the plum pudding model?
An older theory regarding the model of an atom – Scientists used to believe that atoms consisted of spheres of positive charge with electrons stuck to them like plums in a pudding.
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What did the alpha particle scattering experiment in which Geiger, Marsden + Rutherford fired alpha particles at thin gold foil suggest?
Most of the atoms passed through the foil (most of the atom is empty space). Some of the alpha particles were deflected through small angles (nucleus had a pos charge) + a few rebound through large angles (nucleus = large + pos).
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What is the change in the nucleus and the particle emitted in alpha decay?
Nucleus loses 2 protons + 2 neutrons. 2 protons + 2 neutrons are emitted as an a particle. The atomic number goes down by 2 + the mass number goes down by 4.
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What is the change in the nucleus and the particle emitted in beta decay?
There is no change in the atomic number or the mass number. A gamma ray is an electromagnetic wave released from the nucleus with no charge or mass.
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Describe an alpha particle and what it can be stopped by.
Relatively large (has lots of collisions with atoms), strongly ionising + don’t penetrate far into a material, positive charge + are deflected by electric + magnetic fields. They can be stopped by a thin sheet paper/human skin/few cm of air.
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Describe beta particles
Much smaller + faster than a particles so are less ionising, penetrate further, have a negative charge + are deflected by electric + magnetic fields in the opposite direction to a particles. Blocked by a few metres of air/thin sheet of aluminium.
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Describe gamma rays.
Electromagnetic waves that travel far into material before colliding with an atom. Weakly ionising, very penetrating, not deflected by electric/magnetic fields + are blocked by several cm of lead/ metres of concrete are needed to absorb most of the r
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What happens to the count rate of a radioactive sample over time?
It decreases over time and depends on the isotope. The count rate measures the radioactivity of a sample of a radioactive material.
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What is the idea of a half-life used for?
To measure how quickly the radioactivity decreases. It is the time taken for the count rate from the original isotope to fall to half its initial value (time taken for the number of unstable nuclei sample to halve.
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What are alpha sources used for?
They are used in smoke alarms. The alpha particles are not dangerous because they are very poorly penetrating. The source needs a half-life of several years.
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What are Beta sources used for?
Thickness monitoring in the manufacture of things i.e. paper or metal foil. Alpha particles would be stopped by a paper + all gamma rays would pass through it. Source needs half-life of many years so that decreases in count rate are due to the paper.
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What are gamma and beta sources used as in medicine?
As tracers. The source is injected/swallowed by the patient. Its progress around the body is monitored by a detector outside the patient. The source needs a half-life of a few hours so that the patient isn’t exposed to unnecessary radioactivity.
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Radioactive dating is used to find the age of ancient material. Carbon dating is used to find the age wood and other organic materials. Uranium is used to find the age of igneous rocks.
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What is a nuclear fission?
The splitting of an atomic nucleus. There are two fissionable isotopes commonly used in nuclear reactors; uranium-235 and plutonium-239. Most use uranium.
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Why isn’t naturally occurring Uranium used?
As naturally occurring uranium is mostly uranium-238, which is non-fissionable. Most nuclear reactors use “enriched” uranium that contains 2-3% uranium-235.
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What has to happen for a fission to occur?
The uranium-235 or plutonium-239 nucleus must absorb a neutron. The nucleus then splits into two smaller nuclei. In this process 2 or 3 neutrons are emitted and energy is released. This releases much more energy than a chemical process (i.e. burning)
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When does a chain reaction occur in neutron fission?
A chain reaction occurs when each fission event causes further fission events. In a nuclear reactor the process is controlled, so one fission neutron per fission on average goes on to produce further fission.
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What is nuclear fusion?
The process of forcing two nuclei close enough together so they form a single larger nucleus. It can be brought about by making two nuclei collide at very high speed. Fusion is the process by which energy is released in stars.
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What are the problems with producing energy from nuclear fusion in reactors?
Nuclei approaching each other will repel one another die to their positive charge. To overcome this, they must be heated to very high temps (Reaction has to contained by a magnetic field) to have enough energy to overcome the repulsion + fuse.
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What is the major source of background radiation?
Radon gas which seeps through the ground from radioactive substances in rocks deep underground. Radon gas emits alpha particles, so is a health hazard if breathed in.
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What are other sources of background radiation?
Cosmic rays from outer space, food + drink, air travel + nuclear weapons testing. Medical sources of background radiation include X-rays as these have an ionising effect as well as radioactive substances.
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What is done with uranium and plutonium after it is used in a nuclear reactor?
Uranium + plutonium are chemically removed from used fuel rods from nuclear reactors as these substances can be used again. The remaining radioactive waste must be stored in secure conditions for many years.
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What should workers do to reduce exposure to nuclear radiations?
Keep as far as possible from sources of radiation, spend as little time exposed as possible + shield themselves with materials such as concrete and lead.
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What do most scientists believe about the creation of the universe?
Created by Big Bang about 13 bill years ago. At first the universe was a hot glowing ball of radiation. In the first few mins the nuclei of the lightest elements formed. As the universe expanded over mills of years its temp fell + uncharged atoms wer
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How was the universe before galaxies and stars formed?
A dark patchy cloud of H + He. Eventually dust and gas were pulled together by gravitational attraction to from stars. The resulting intense heat started off nuclear fusion reactions in the stars, so they began to emit visible light + other radiation
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What is a galaxy?
A galaxy is a collection of billions of stars held together by their own gravity. There are billions of galaxies in the universe with vast empty space between them. Our sun is one the many billions of stars in the Milky Way.
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How does the formation of a star begin?
Gravitational forces pull clouds of dust and gas together to form a protostar. The protostar becomes denser + the nuclei of hydrogen + other light atoms start to fuse together. Energy is released in the process so the core gets hotter + brighter.
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Why do stars radiate energy and how long can this stage last?
Stars radiate energy because of hydrogen fusion in the core. This stage can continue for billions of years until the star runs out of hydrogen nuclei – main sequence.
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Why are stars in the main sequence stable?
As the inward force of gravity is balanced by the outward force of radiation – called a main sequence star. Eventually a star runs out hydrogen nuclei, swells, cools down + turns red.
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What happens to a star similar in size to our sun (low mass)?
In a red giant, helium and other light elements fuse to form heavier elements. Fusion stops and the star will contract to form a white dwarf. Eventually no more light is emitted and the star becomes a black dwarf.
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What will happen to a star much larger than our sun?
It will swell to become a Red Supergiant which continues to collapse. Eventually the star explodes in a supernova + the outer layers are thrown out into space. The core is left as a neutron star. If this is massive enough it becomes a black hole.
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What is a black hole?
If a neutron star becomes massive enough then it will become a black hole. The gravitational field of a black hole is so strong that not even light can escape from it.
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How are chemical elements formed?
Chemical elements are formed by fusion processes in stars. The nuclei of lighter elements fuse to form the nuclei of heavier elements. The process releases large amounts of energy.
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How are elements heavier than iron formed?
Elements heavier than iron are only formed in the final stages of the life of a big star. This is because the process requires the input of energy. All elements get distributed through space by the supernova explosion.
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How are the chemical elements distributed through space?
The presence of the heavier elements in the sun and inner planets is evidence that they were formed from debris scattered by a supernova.
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## Other cards in this set

### Card 2

#### Front

What can a velocity-time graph show?

#### Back

Acceleration given by gradient. Distance travelled shown by calculating area of shape beneath gradient. If line=horizontal, acceleration=0 + object is moving at a steady pace. Negative gradient = deceleration.

### Card 3

#### Front

What can a distance-time graph show?

### Card 4

#### Front

What are action and reaction forces and how can they be applied?

### Card 5

#### Front

What is resultant force and what happens when the resultant force is zero?