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150 Cards in this Set
- Front
- Back
Forces act in |
Forced act in pairs. |
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When a force acts in one direction |
an equal and opposite force is exerted in other direction |
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what is a reaction force? |
When 2 forces interact they are equal and opposite in direction e.g. a person exerts a force on the chair but the chair applies an equal force upwards on the person, a reaction force. |
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Weight is a |
force measured in newtons. |
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weight and mass |
Don’t confuse mass and weight as mass is actually the amount of ‘stuff’ that makes up an object measured in kilograms. |
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The equation to work out weight is... |
Weight is the force calculated by Weight (N) = Mass (kg) x Gravitational field strength (N/kg) |
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The gravitational field strength of earth is |
The gravitational field strength on Earth is taken as 10N/kg. |
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The speed of an object is |
distance travelled in seconds |
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The gradient of a line on a distance time graph represents |
speed |
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On a distance time graph, the greater the gradient of line |
the greater the speed |
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On a distance time graph if the line is horizontal |
the object is stationary |
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On a distance time graph, if the object is moving at a constant speed the line is |
a straight line sloping upwards |
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How do we calculate the speed of an object? |
speed (m/s)= distance traveled (m) ------------------------------- Time taken in (s) |
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Velocity is |
speed in a given direction |
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If an object changes direction... |
it changes velocity even if the speed remains the same |
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Therefore if the velocity of an object changes |
it accelerates |
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Acceleration= |
a (m/s2)= v-u ------- t where v is the final velocity, u is the initial velocity and t is the time |
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The gradient of the line on a velocity time graph represents |
acceleration |
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The steeper the gradient of a velocity time graph |
the greater the speed |
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if the line on a velocity time graph is horizontal the object is |
travelling at a steady speed so the acceleration is zero |
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The distance travelled by an object is given by |
the area under the line of its velocity time graph |
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What is the resultant force? |
single force that would have the same effect on the object as all the original forces acting together. |
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When the resultant force of an object is zero... |
if object is at rest it will stay at rest if the object is moving it will carry on moving at the same speed in the same direction |
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when the resultant force of an object is not zero, |
there will be acceleration in the direction of the force |
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if the resultant force is not zero the object will, |
accelerate in the direction of the resultant force if it was at rest if object is moving in same direction of resultant force it will accelerate in that direction if object is moving in opposite direction of resultant force it will decelerate |
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A resultant force always causes an |
acceleration |
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Acceleration is the change in velocity |
an object can accelerate by changing =its direction even if it is going at a constant speed. so a resultant force is needed to make the object change direction |
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resultant force is found by |
f=m x a f= force (N) m= mass(kg) a=acceleration (m/s2) |
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What is the stopping distance? |
the distance traveled during the drivers reaction time plus the distance it travels under the braking force Stopping distance = thinking distance + braking distance |
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thinking distance is increased |
if driver is tired or under influence of drugs or alcohol |
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Balanced forces occur when |
an object is stationary or moving at a constant speed. The faster an object is moving the bigger the frictional forces acting on it. |
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Braking distance can be increased by |
poorly maintained roads or bad weather conditions condition of car i.e if the brakes or tyres of car are worn |
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An object falling through a fluid or gas will initially accelerate due to the force of gravity as |
there is a resultant force acting on it which is gravity |
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The force of gravity can be referred to as |
weight |
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to work out the weight you do |
w= m x g where w is the weight (N) as it is the force m is the mass (kg) g is the acceleration due to gravity (m/s2) |
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When an object falls through a fluid, |
the fluid exerts a drag force on the object resisting its motion |
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in a fluid, the faster the object falls |
the bigger the drag force becomes until eventually it will equal the weight of the object. resultant force is now zero so the body stops accelerating. It moves at a constant speed called Terminal velocity |
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What is terminal velocity? |
The constant speed that a freely falling object eventually reaches when the resistance of the medium through which it is falling prevents further acceleration. |
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what is the extension? |
the increase in the length from the original of the spring |
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If an object is elastic, how does it behave? |
an object that regains its original shape when the forces deforming it are removed |
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the extension is directly proportional to |
the force applied |
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If we apply too big of a force, |
the line begins to curve because have exceeded the Limit Of Proportionality |
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Hookes law |
that the extension is directly proportional to the force applied provided the limit of proportionality is not exceeded. |
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Hookes law equation is |
f=k x e f= force (N) k= the spring constant of spring in (N/m) e= extension (m) |
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the stiffer the spring |
the greater its spring constant |
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when an elastic object is stretched |
work is done. this is stored as elastic potential energy in the object |
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when the stretching force is removed |
this stored energy is released |
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Whenever an object starts to move |
a force must have been applied to it |
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when a force moves an object |
energy is transferred and work is done |
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Work done is equal to |
the energy transferred |
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work done is calculated using |
w=f x d w= work done (J) f= force (N) d= distance (m) |
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what is gravitational energy |
energy stored in an object because of its position in the Earths gravitational field strength |
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When an object is moved vertically upwards, |
it gains gravitational potential energy equal to the work done on it by the lifting force |
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change in gravitational potential energy is calculated using |
Ep = m x g x h Ep is change in gravitational potential energy (J) m is the mass (kg) g is the gravitational field strength (N/kg) h is height (m) |
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Power is... and can be calculated using... |
power is the rate of energy transferred p= e ----- t p is power (W) e is energy (J) t is time (s) |
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All moving objects have |
kinetic energy |
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the greater the mass of an object, the greater the speed and |
the more kinetic energy it has |
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kinetic energy equation |
Ek= 1/2 x m x v2 Ek is kinetic energy (J) m is mass (kg) v is speed (m/s) |
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Summary of elastic potential energy |
if object regains shape after being stretched or squashed it is described as elastic work is done on object to stretch or squash it, so the energy transferred to it is elastic potential energy energy. when object returns to its original shape, this energy is released |
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The greater the mass of object, the greater the speed and greater its |
momentum |
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Momentum is calculated doing |
p=m x v p= momentum in (kg m/s) m= mass (kg) v=velocity (m/s) |
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whenever an object interacts |
the total momentum before is equal to the total momentum afterwards provided no external forces act on them |
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What is the conservation of momentum? |
the total momentum before the interaction is equal to total momentum after |
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if one side of the momentum calculation is positive |
the other side is negative |
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When two objects are at rest |
their momentum is at zero |
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when a force acts upon an object that is moving or is able to move |
the momentum changes |
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If the impact time is short |
the forces acting on the object are large. As the impact time increasing the force becomes less |
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When two vehicles collide |
the both exert equal and opposite forces on eachother and their total momentum is unchanged |
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When two electrically insulating objects are rubbed together |
electrons are rubbed off one material and deposited on the other |
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Because the electrons have an negative charge |
the material that gains the electrons becomes negatively charged, so the one that loses them becomes positively charged. This is called charging by friction |
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a diode |
allows current through it in one direction |
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light emitting diode |
emits light when current passes through it |
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a fixed resistor |
limits current in circuit |
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variable resistor |
allows the current to be varied
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a fuse |
designed to melt and therefore break the circuit if the current through it is greater than a certain amount |
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LDRs |
LDRs (light-dependent resistors) are used to detect light levels, for example, in automatic security lights. Their resistance decreases as the light intensity increases:In the dark and at low light levels, the resistance of an LDR is high, and little current can flow through it.In bright light, the resistance of an LDR is low, and more current can flow through it. |
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thermistor |
Thermistors are used as temperature sensors, for example, in fire alarms. Their resistance decreases as the temperature increases. At low temperatures, the resistance of a thermistor is high, and little current can flow through them.At high temperatures, the resistance of a thermistor is low, and more current can flow through them. |
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potential difference = |
v= W ----- Q v is p.d (v) w is work done (J) Q is charge (C) |
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Resistance is the opposition |
to current flow |
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resistance is calculated using |
R= V ---- i where r is the resistance (in ohms) v is p.d (v) i is current (A) |
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Ohms law |
the current is directly proportional to the potential difference across the resistor. |
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Any component that obeys ohms law is called an |
Ohmic conductor |
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on a current potential difference graph for a filament bulb |
the line is a curve so current is not directly proportional to the p.d. resistance of filament bulb increases as current increases. this is because the resistance increases as the temp increases |
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in a series circuit, the components are connected one after another so |
if there is a break in the circuit anywhere , charge stops flowing |
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current is |
I= V --- R |
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the bigger the resistance of a component |
the bigger its share of the supply p.d |
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in a parallel circuit |
each component is connected across the supply so if there is a break in one part of circuit charge can still flow in other parts |
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each component is connected across the p.d supply so |
p.d across all components is the same |
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the bigger the resistance of the component |
the smaller the current through it |
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Frequency of the UK mains supply is |
50Hz which means it changes direction 50 times each second |
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therefore the voltage of UK mains supply is |
230 volts |
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the frequency of an a.c supply can be determined from an oscilloscope trace using equation |
f= 1 --- t f is frequency (Hz) t is time taken for one cycle (s) |
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why is the outer cover of a three pin plug made of plastic or rubber? |
because both these materials are good electrical insulators |
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the pins of the plug are made of brass as |
brass is a good electrical conductor as it is hard and will not rust or oxidise |
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the brown wire is |
the live wire |
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the blue wire in the |
neutral wire |
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the yellow and green wire is |
the earth wire |
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appliances with metal cases must be |
earthed |
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appliances with plastic cases do not need to be earthed because |
they are said to be double insulated |
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in a cable, the more current to be carried |
the thicker the cable |
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why do appliances with metal cases need to be earthed? |
because if a fault develops and the live wire touches the metal cause, the case becomes live and could give and electric shock to anyone who touches it |
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the rating of the fuse should be slightly higher than the normal working current of the appliance because |
if it is much higher, it will not melt soon enough to break the circuit and if it is not higher than the normal current it will melt as soon as the appliance is switched on |
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what is a circuit breaker? |
an electromagnet switch that opens and cuts off the supply if the current is bigger than a certain value |
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what is a RCCB? (residual current circuit breaker) |
cuts of the current in the live wire if it is different to the current in the neutral wire. it works faster than a fuse or ordinary circuit breaker |
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when a charge flows through an appliance, electrical energy is transferred to other forms. in a resistor |
electrical energy is transferred to the resistor so the resistor becomes hotter |
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the nuclei of a radioactive substance is |
unstable |
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how does the nuclei of a radioactive substance become stable? |
Radioactive Decay |
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Name the three types of radiation emitted |
alpha, beta , gamma |
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Background radiation is |
around us all the time. it is from radioactive substances in environment, from space, and devices like x rays |
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Rutherford, Geiger and Marsden devised an |
alpha particle scattering experiment, in which they fired alpha particles at thin gold foil |
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What did they discover in Rutherfords experiment |
most of the alpha particles passed straight through the foil, this means that most of the atom is just empty space. some of the alpha particles were deflected through small angles which suggests that the nucleus has a positive charge. a few rebound through very large angles. this suggests that the nucleus has a large mass and a very large positive charge |
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What happens in alpha decay |
the nucleus loses 2 protons and 2 neutrons |
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What happens in beta decay? |
a neutron in the nucleus changes into a proton and an electron |
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an isotope is |
same element with different number of neutrons in nucleus |
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Atomic number |
number of protons in atom |
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Mass number |
protons plus neutrons |
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Beta is a |
high speed electron from nucleus, emitted when neutron in nucleus changes to a proton and electron.
0 Represented as B -1 |
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Gamma ray is |
electromagnetic wave released from nucleus with no overall charge |
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Alpha is |
made up of two protons and two neutrons when a nucleus emits alpha particle the atomic number goes down by two and the mass number goes down by four |
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What is ionisation? |
when nuclear radiation travels through a material it will collide with the atoms of a material and knock the electrons off creating ions |
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Alpha particles properties |
relatively large so have lots of collisions with atoms, they are strongly ionising. they can be stopped by thin sheet of paper human skin or few cm of air alpha particles have positive charge so are deflected by electric and magnetic fields Very ionising as once in body can not escape out |
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beta particle properties |
much smaller and fast than alpha so less ionising and penetrate further blocked by few metres of air or thin sheet of aluminium negative charge and are deflected by electric and magnetic fields in opposite direction to alpha particles |
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Gamma particle properties |
electromagnetic waves so will travel long way through material before colliding with atom weakly ionising very penetrating stopped by several cm of lead or several metres of concrete not deflected by magnetic or electric fields |
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What is the half life of a radioactive isotope? |
the average time it takes for the number of nuclei of the isotope in a sample to halve |
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the activity of a radioactive source is |
number of nuclei that decay per second |
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number of atoms of radioactive isotope and activity |
both decrease by half every half life |
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Alpha sources are used in |
smoke alarms |
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beta sources used for |
thickness monitoring |
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gamma and beta sources used as |
traces in medicine. it is swallowed or injected and its progress around the body is monitored by a detector outside the patient |
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radioactive dating is used for |
finding the age of ancient material. carbon dating used to find age of wood and other organic material uranium dating used to find age of igneous rocks |
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nuclear fission is the |
splitting of atoms nucleus |
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what two fissionable isotopes are commonly used in a nuclear reactor? |
uranium-235 and plutonium-239 uranium 235 is most commonly used |
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Nuclear fission process |
for 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 two or three more neutrons are emitted and energy is released. the energy released in such a nuclear process is much greater than the energy released in a chemical process such as burning |
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When does a chain reaction occur? |
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 this takes place in a reaction chamber/ fuel rods |
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What is nuclear fusion? |
process of forcing two nuclei close enough together so they form one single larger nucleus |
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nuclear fusion happens as |
they make two light nuclei collide at very high speed |
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fusion is the process by which energy is released in |
stars |
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nuclei approaching eachother will repel due to their positive charge so to over come this |
the nuclei must be heated at very high temperatures and reaction must be contained by a magnetic field |
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to reduce exposure to radiation, workers must |
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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most scientists believe earth was created by big bang |
13 billion years ago |
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protostars are formed by |
dust and gas being pulled together by gravitational forces |
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the protostar becomes denser and |
the nuclei of hydrogen and other light elements fuse together. energy is released from process so core gets brighter and hotter |
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stars radiate energy because of |
hydrogen fusion in core. this stage can continue for billions of years until the star runs of out hydrogen nuclei. |
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a main sequence star is when |
the star is stable because the inward force of gravity is balanced by the outward force of radiation from core |
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eventually a star runs out of hydrogen nuclei... |
swells, cools down and turns red |
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Now, if the main sequence star has a low mass... |
is now 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 so it becomes a black dwarf |
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Now if the main sequence star has a larger mass |
it is a red super giant which continues to collapse eventually the star explodes into a supernova the outer layers are thrown out into space and the core is left as a neutron star if this is massive enough it becomes a black hole the gravitational field strength of the black hole is so strong that not even light can escape from it |
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chemical elements are formed by |
fusion processes in stars |
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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 |
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The presence of heavier elements in the sun and inner planets are |
evidence that they were formed from debris scattered by supernova |