Physics Module 2

Revision Cards for Module/Unit 2 of Physics. Needed for January Mock Exams and May GCSE's.

Physics Module 2

Motion - 1.1 Distance Time Graphs

• Graphs can be used to describe the motion of an object
• Distance time graph shows the distance travelled by an object against the time taken. Would you believe it? God, the clue is in the name duh brain. If you forget this I will kill you.
• The Speed is the distance travelled each second.
• The line represents speed. Steeper line = greater speed
• Horizontal line = object is stationary
• Constant speed = line that is straight. Gradient does not change.

The Equation (be scared - fear the equation)

Speed = Distance Travelled

Time

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Physics Module 2

Motion - 1.2 Velocity and Acceleration

Velocity - The speed of an object in one direction. (ahead) If the object changes direction, although the speed remains the same the velocity changes. If the velocity of an object changes then we say it accelerates.

The EQUATION!!!! duh duh duh

Acceleration (m/s²) = Final Velocity (m/s) - Initial Velocity (m/s)

Time Taken for Change (s)

a = v - u

t

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Physics Module 2

Motion - 1.3 More about Velocity - Time Graphs

Velocity-Time Graphs - Shows the Velocity (y-axis) against the Time (x-axis), the                                                  gradient of a line represents acceleration - the steeper etc. If                                            the line is hoorizontal then the acceleration is zerpo, the object                                          is at a constant speed.

THE AREA  UNDER THE LINE ON A VELOCITY-TIME GRAPH REPRESENTS THE DISTANCE TRAVELLED.

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Physics Module 2

Motion - 1.4 Using Graphs

Photocopy this section and stick it in. I can't replicate the notes.

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Physics Module 2

Forces - 2.1 Forces Between Objects

Forces = measured in Newtons

Forces always exert 'ACTION AND REACTION' forces on each other. This means that if object A acted on object B, object B would react with an equal amount of an opposite force to A. e.g.

• Car hits a barrier. Car exerts force - barrier exerts equal and opposite directional force.
• Placing a book on a table. Book has a vertically downward force on table - table exerts equal opposite force on the book.
• Car is driving. Tyre on ground pushes backwards - equal and opposite force from the ground which pushes car forward.

FORCES HAVE BOTH SIZE AND DIRECTION.

A FORCE CAN CHANGE THE SHAPE, AN OBJECT'S MOTION OR IT'S STATE OF REST.

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Physics Module 2

Forces - 2.2 Resultant Force

Resultant Force - The single force that would have the same effect on the object as all                                 the original forces acting together.

When the resultant force is zero there will be no change on the objecs momentum. If it was at rest, it will stay at rest. If it was moving it will continue to move at a constant rate in the same direction.

When the resultant force is not zero there will be an ' acceleration' (not your typical acceleration - although it could be it just depends) in the direction of the force. This means that if an object is at rest, it will accelerate in the direction of the force. If the object is moving in the same direction as the resultant force it will accelerate in that direction. If the object is moving in the opposite direction to the resultant force it will decelerate.

Just to cheer you up whilst revising picture Mr Entwistle having his balls cut off by a crab. Whilst dancing the macarena.

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Physics Module 2

Forces - 2.3 Force and Acceleration

A resultant force always causes an acceleration (a deceleration is a negative acceleration). black american voice If there is no acceleration then there is no resultant force. Hmhmm.

Acceleration - A change in velocity. An object can also accelerate by changing its direction even                        though it hasn't changed it's speed. This means a resultant force is needed to                        change direction.

EQUATION TIME: (duh duh duh duh duh DUH!)

Force (N) = Mass (m) x Acceleration (m/s²)

F = m x a

General Rule (of thumb hehehe) - the greater the resultant force the greater the acceleration. THe bigger the mass, the bigger the force required to give it a particular acceleration.

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Physics Module 2

Forces - 2.4 On the Road

Stopping Distance (of a vehicle) -  The distance it travels during the driver's reaction time                                                                 (thinking distance) plus the distance it travels under the                                                             braking force (braking distance).

Thinking Distance (of a vehicle) - This is the distance travelled before a driver to reacts adn                                                            applies the breaks. It can be hindered if the driver is tired or                                                        is under the influence of alcohol or drugs.

Braking Distance (of a vehicle) - This is the distance travelled for the car to stop after the                                                               breaks have been applied. It can be increased by poorly                                                             maintained roads, bad weather conditions and worn tyres or                                                       brakes.

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Physics Module 2

Forces - 2.5 Falling Objects

If an object is in free fall the resultant force acting is Gravity.

EQUATION TIME!!!! You're favourite ...

Force (N) = Mass (kg) x Acceleration (m/s²)

F = m x a

BECOMES

Weight (N) = Mass (kg) x Acceleration (m/s²)

W = m x g

• If an object on Earth isn't falling, g is called the Gravitational Field Strength (N/kg)
• When an object falls through a fluid, drag force is exerted resisting it. The faster the fall, the more drag force until eventually they are equal to object's weight. There is now no resultant force so there is no longer any acceleration. This constant velocity is called terminal velocity.

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Physics Module 2

Forces - 2.6 Stretching and Squashing

Extension - The increase of a length of a spring  when stretched. (Objects that behave                                like this are called elastic objects. These objects will return to their original                              shape when the forces acting on it are removed.)

EXTENSION IS DIRECTLY PROPORTIONAL TO THE FORCE APPLIED ON IT. This equates to a straight line passing through the origin. We can however exceed the limit of proportionality the line will curve.

Hooke's Law

This is what is stated above.

• EQUATION - (running out of space bare with).

Force (N rep. F) = Spring Constant (N/m rep. k) x Extension (m rep. e)

• The stiffer a spring the greater the spring constant
• Stretched elastics = work done. Stored as elastic potential energy in the object.
• When this force is removed the energy is released.

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Physics Module 2

Forces - 2.7 Force and Speed Issues

• Fuel economy - the reduction of speed used to reduce amount of fuel used to travel a particular distance.
• Fuel economy can also be increased by making a car more streamlined so reducing air resistance.
• Speed camera's are used to calculate the average speed of a vehicle. Pairs can be used to work out the speed of a car between a particular distance. Drivers exceeding the limit can get fined or lose their lisence.
• Skidding - the brakes are applied too harshly. It locks the wheels and slides along road surface. Stopping distance is increased.
• Anti-skid surfaces are used to reduce or prevent skidding. No **** sherlock. They increase the friction between tarmac and tyres and are placed in areas where cars are likely to brake.

Notice how I used rainbow colours to cheer you up. :)

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Physics Module 2

Work, Energy and Momentum - 3.1 Energy and Work

When a force moves an object energy is transferred and work done. When work is done moving the object, the supplied energy is transferred to the object so the work is equal to the energy transferred. Both of these have the unit, J (if you don't know what this means ... you should). You still with me?

EQUATION

Work Done (J) = Force (N) x Distance (m) moved in the direction of the force

W = F x d

Work Done to overcome friction is mainly transferred into energy by heating. When the brakes are applied to a vehicle, friction between the brake pads and the wheel discs opposes the motion of the wheel. The kinetic energy of the vehicle is transferred into energy that heats the brake pads and the wheel discs as well as the surrounding air.

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Work, Energy and Momentum - 3.2 Gravitational Potential Energy

Gravitational Potential Energy - Stored energy in an object because of its position in the Earth's Gravitational field. When an object goes up it gains g.p.e equal to the work done.

EQUATION -

Change in G.P.E (J) = Mass (kg) x Gravitational Field Strength (N/kg) x Change in Height (m)

E = m x g x h

POWER EQUATION

Power (W rep. P) = Energy (J rep. E)

Time (s rep. t)

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Physics Module 2

Work, Energy and Momentum - 3.3 Kinetic Energy

The Greater the Mass and Speed of said object the more kinetic energy.

EQUATION - duh duh duuuuuh

Kinetic Energy (J) = ½ x Mass (kg) x Speed (m/s)

E = ½ x m x v²

This is pretty much it. So yeah just include a pretty picture to make you feel better.

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Physics Module 2

Work, Energy and Momentum - 3.4 Momentum

The greater the mass and the greater the velocity of an object the greater it's momentum.

EQUATION -

Momentum (kg m/s) = Mass (kg) x Velocity (m/s)

p = m x v

Conservation of Momentum

Pretty much what it says. When objects collide the total momentum before the collision is equal to the total momentum after the collision (providing no external forces act on them). If you wanted to be fancy and Sheldon-like you could say that the total change in momentum is zero. The interaction could be either a collision or an explosions. Guess what's coming up next. ;)

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Physics Module 2

Work, Energy and Momentum - 3.5 Explosions

When two objects are at rest their momentum is zero. In an explosion the objects move apart with equal and oppposite momentum (like velocity). One momentum is positive and the other is negative so the total momentum after said explosion is zero. The big zilch.

Good example (because we need that!)

A gun firing. The bullet moves off in one direction and the gun recoils with equal and opposite force. When two objects push apart they have different speeds depending on the mass bt equal and opposite momentums that equal zero.

TIP - IT OFTEN HELPS TO DRAW A DIAGRAM (IN CALCULATIONS INVOLVING THE CONSERVATION OF MOMENTUM AND COLLISIONS AND EXPLOSIONS).

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Physics Module 2

Work, Energy and Momentum - 3.6 Impact Forces

• When a force acts on an object that it able to move/is moving (delete as appropriate) it's momentum changes.
• For a particular cahnge in momentum the longer the time taken for the change, the smaller the force that acts.
• In a collision , the momentum of an object often becomes zero during the impact - the object comes to rest.
• If the impact time is short the forces on the object are large. As the impact time increases the forces become less.
• Crumple zones in cars are desgined to fold in a collision. THis increases the impact time and so reduces the force on the car adn teh people in it.

I feel pretty oh so pretty I feel pretty and witty and WISEEE!!!!

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Physics Module 2

Work, Energy and Momentum - 3.7 Car Safety

To reduce the force on the car occupants there are -

• Crumple Zones and Side Impact Bars
• Seat Belts and Air bags which spread the forces on the human body over a larger area.(If a drvier hit his head on an airbag it changes momentum slowly so itw ouldn't be so forceful on the head than if it changed momentum quickly by hitting the steering wheel.
• Seat belts stop the wearer from being flung forward and hitting their heads. It stretches to slightly to increase impact time and reducing the force.

Police can calculate the speed of the car at the crash by taking measuerements and using the conservation of momentum.

TIP - MAKE SURE YOU CAN EXPLAIN HOW EACH ITEM WORKS IN TERMS OF SPREADING OUT AND REDUCING THE FORCES ON THE OCCUPANTS.

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Physics Module 2

Current Electricity - 4.1 Electrical Charges

When two insulating (electrically) materials are rubbed electrons are tranferred. The direction depends on the materials.

• Material thats gained electrons = negative charge
• Material that has lost electrons = positive charge
• The process is called CHARGING BY FRICTION
• Opposites attract. Like's repel.
• The bigger the distance between the two objects, the weaker the force.

Bt you knew this anyway you smart thang!

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Physics Module 2

Current Electricity - 4.2 Electric Circuits

Every component has a circuit symbol. These are used to shwo how a ccircuit is put together. Copy and paste the picture in or learn it you know.

PLACE PICTURE FROM BOOK HERE.

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Physics Module 2

Current Electricity - 4.3 Resistance

The current is measured with an AMMETER. They are always placed in series.  The unit is an amp (A)

The potential difference/voltage is measured with a Voltmeter. They are always placed in parallel with component. The unit is the volt (V)

LOADS OF EQUATIONS!!!! For the rest look at page 53 in Physics Revision Guide.

Voltage (V) = Work Done (W and J)

Charge (Q unit = C)

Ohm's Law

If resistor is at a constant temperature then the current-potential difference will be a straight line on graph through origin. Current = Directionally proportional  Voltage across resistor. This is Ohm's Law. Any component that obeys Ohm's Law is known as an Ohmic Conductor!

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Current Electricity - 4.4 More Current-Potential Difference Graphs

• The line on a current-voltage graph for a filament buld is an s-shaped curve. Not directionally proportional. This shows the filament resistance increases as the current increases. This is because resistance increases as temperature increases. Reversing voltage makes no difference
• The current through a diode flows in one direction only. In reverse direction the diode resistance is so high the current is zero.
• As the light falling on it get's brighter , the resistance of a 'Light-Dependant Resistor' (LDR) decreases.
• As the temperature goes up, the resistance of a thermistor goes down.

FIND GRAPH IMAGES AND GLUE DOWN HERE!!!!

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Current Electricity - 4. 5 Series Circuits

Components are connected one after the other (if a break is in the circuit then the charge ain't gonna flow.

Current through each component is the same because there is no choice of route.

The current depends on the potential difference of the supply (cell) and the resistance of the circuit.

EQUATION!!!!! (You're getting tired of these I know)

Current (A rep. I) = Potential Difference (V rep. V)

Resistance (Ω rep. R)

• The Voltages are shared so each components voltage adds up to the total for the circuit.
• The resistances in series add up to give the total resistance.
• The bigger a components resistance, the bigger it's share of voltage.
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Current Electricity - 4.6 Parallel Circuits

In a parallel circuit, components are connected across the supply so if tehre is a break in one part of the circuit, charge can still flow in other parts. Each component has the same voltage. The circuit contains junctions so different amounts of charge can flow through different components. The current through each component depens on its resistance. The bigger the resistance of a component the smaller the current through it.

EQUATION!!!

Same one as previous card. Cos I'm lazy.

THE TOTAL CURRENT THROUGH THE WHOLE CIRCUIT IS EQUAL TO THE SUM OF THE CURRENTS THROUGH SEPERATE COMPONENTS.

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Mains Electricity - 5.1 Alternating Current

Direct Current - A current that travels around the circuit in one direction. (no pun                                                  intended). This is done by cells and batteries. Shown as dc.

Alternating Current -  A current that passes in one direction then reverses and passes in the                                         other direction. Done by mains electricity. Shown as ac.

The UK Mains supply has a frequency of 50 Hert (Hz) which means it changes direction 50 times a second. The voltage is 230 V.

A live wire (mains supply) alternates between a positive and a negative potential with respect to the neutral wire. The neutral wire stays at zero volts. The live wire alternates between peak voltages of  + 325 V and - 325 V. In terms of electrical power this is the equivalent of a voltage/potential difference of 230V. Look at graph p 57 to really make sense of this.

The frequency of an ac supply can be determined from an oscillope trace using the equation:

Frequency (Hz rep. f) = 1

Time Period (secons rep. T)

BECAUSE YOU WERE STRUGGLING. THE PEAK VOLTAGE OF AN ALTERNATING P.D. IS THE MAXIMUM VOLTAGE MEASURED FROM ZERO VOLTS.

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Mains Electricity - 5.2 Cables and Plugs

Electrical appliances are connected to a socket via a cable and a three-pin plug

• The three pin plug outer cover is made of plastic and rubber - insulators.
• The pins are made of brass - won't rust/oxidise and a good conductor.
• The Earth Wire (green and yellow) is connected to the longest pin (top one). Two pin plugs don't have this.
• The Brown Wire is Connected to the live pin
• The Blue Wire is connected the neutra pin.
• The cable grip should be fastened tightly over the cable. No bare wires showing inside the plug and the correct cable must be connected firmly to the correct pin.

Further Notes

• Appliances with a metal case must be earthed. The case is attatched to the earth wire.
• Appliances with plastic cases do not need to be earthed. This is because they are already insulated.
• Cables of different thicknesses are used for different purposes. The more current = the thicker a cable.
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Mains Electricity - 5.3 Fuses

Appliances with a metal case must be earthed. Otherwise if a fault occurs and the live wire touches the metal case the case becomes live and is capable of emitting an electric shock.

Fuse - This cuts the appliance off from the live wire if it 'blows'. It is connected in series with the                live wire. It happens by melting ('blowing') if a large current lows through the earth wire and            disrupting the supply. The rating should always be slightly higher than the normal currentof            the appliance. Too high = not melt soon enough.

Circuit Breakers - Alternative to a fuse. Electromagnetic switch that opens and cuts off the                                     supply if the current is bigger than a certain value.

Residual Current Circuit Breaker (RCCB) -  Faster than a fuse and a circuit breaker. It works                                                                        by cutting off the current in the live wire if it is                                                                            different to the current in the neutral wire.

YAY Finished!

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Mains Electricity - 5.4 Electrical Power and Potential Difference

Electrical appliance tranfers electrical energy into other forms of energy. The rate of this is called the power.

EQUATION!!!! Darth Vadar theme tune accompaniment.

Power (W rep. P) = Energy Transferred (J rep. E)

Time (s rep. t)

However it is more common to calculate the current in an appliance and the voltage across it.

Power (W rep. P) = Current (A rep. I) x Voltage (V rep. V)

• All appliances have a power rating. UK pd of mains supply is 230V
• This equation can be used to work out the normal current through an appliance and so work out the size of fuse. Fuse should be slightly higher than the current.

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Mains Electricity - 5.5 Electrical Energy and Charge

EQUATION!

Charge (C rep. Q) = Current (A rep. I) x Time (s rep. t)

Not essential but worth knowing information

• An electrical current is the flow of charge
• When charge flows through an appliance, electrical energy is tranferred into other forms. e.g In a resistor, electrical energy is tranferred to the resistor so the resistor becomes hotter.

Energy (J rep. E) = Voltage (V rep. V) x Charge (C rep. Q)

Rainbows, unicorns, don't panic. I like pizza.

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Mains Electricity - 5.6 Electrical Issues

• Can occur due to damage.
• Avoid overloading sockets. This can caue overheating and a risk of fire
• Appliances should be handeled safely and never come in contact with water. The cable should always be appropriate for intended use.
• When choosing an appliance, you should consider the power and efficiency rating as well as the cost.
• Filament bulbs and halogen bulbs are much less efficient than low-energy bulbs and do not last as long.
• Electrical equipment should be regularly checked for damage of wear.
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Physics Module 2

The nuclei of radioactive substances are unstable. They become stable by radoactive decay. In this process they emit radiation and turn into other elements.

There are 3 Types of Radiation -

Radioactive decay is a random process.

Background Radiation - This is radiation from radioactive substances in the environment, space                                       and devices such as x-ray tubes.

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Radioactivity - The Discovery of the Nucleus

Plum Pudding Model - What scientists original believed an atom looked like. A sphere of                                               positive charge with electrons scattered in them.

Then Rutherford, Geiger and Marsden devised an 'Alpha Particle Scattering' experiment, in which they fired alpha particles at thin gold foil. There findings -

• Most alpha particles passed through. Means an atom is mainly empty space.
• Some of the alpha particles were deflected by small angles. Nucleus has a positive charge.
• A few rebounded by large angels. Suggested that the nucleus has a large mass and a very large positive charge.

Look at diagram on p 63.

This got rid of the plum pudding model.

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Radioactivity -  6.2 The Discovery of the Nucleus

Plum Pudding Model - What scientists original believed an atom looked like. A sphere of                                               positive charge with electrons scattered in them.

Then Rutherford, Geiger and Marsden devised an 'Alpha Particle Scattering' experiment, in which they fired alpha particles at thin gold foil. There findings -

• Most alpha particles passed through. Means an atom is mainly empty space.
• Some of the alpha particles were deflected by small angles. Nucleus has a positive charge.
• A few rebounded by large angels. Suggested that the nucleus has a large mass and a very large positive charge.

Look at diagram on p 63.

This got rid of the plum pudding model.

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α - The nucleus loses 2 protons and 2 neutrons. These are emitted as an α particle.

β - A neutron in the nucleus changes into a proton and an electron. The elctron created is             emitted.

Ion - A charged atom (lost or gained electrons)

Isotopes - Atoms of the same element with a different number of neutrons

Alpha particle - Two protons and two neutrons. We represent it as ⁴₂α. This means that                                      the atomic number goes down by two and the mass goes down by 4.                                            Radium - Radon. It is equivalent to a Helium atom.

Beta Particle - A high-speed electron, emitted during Beta Decay. It's written as  ⁰e. (- 1                                  under 0). The proton stays in the nucleus so atomic goes up by one. Mass is                              unchanged.  Carbon-14 - Nitrogen + beta particle.

Gamma Radiation - No mass or atomic number change. This is just an electromagnetic                                                 wave released from the Nucleus.

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Ionisation

• Nuclear radioation travels through materials aand collides with the atoms inside. This knocks the electrons off them, creating ions.
• In a living cell this can damage or kill it.

Alpha Particles

• Relatively large, so they have lots of collisions - strongly ionising.
• They don't penetrate far. Can be stopped by sheet of paper, human skin, a few cm of air.
• They have a positive charge and are deflected by electric and magnetic fields.

Beta Particles

• Less ionising and penetrate further. Smaller and faster. A thin sheet of aluminium would stop them.
• Negative charge and are also deflected by magnetic and electric fields but in opposite way.

Gamma Rays

• Eletromagnetic waves so will travel a long way before colliding. Weakly ionising, very penetrative
• Several cm lead, or m of concrete are needed to absorb it.
• They are not deflected by Electronic or magnetic fields.
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Using half-life we can see how radioactive something is. We do this using the count rate. Since an objects radioactivity decreases over time, we see how quickly the count rate falls to zero. However some can take minutes, others millions of years.

HALF-LIFE IS THE TIME TAKEN FOR THE COUNT RATE FOR THE ORIGINAL ISOTOPE TO FALL TO HALF ITS VALUE.

or

HALF-LIFE IS THE TIME TAKEN FOR THE NUMBER OF UNSTABLE NUCLEI IN A SAMPLE TO HALVE.

The half-life is the same for any sample of isotope.

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Alpha Sources

• Smoke Alarms. Not dangerous because not penetrating.

Beta Sources

• Thickness monitoring in manufacturing of paper or metal foil. The source must have a half-life of many years so that decreases in count-rate are due to changes in the thickness of paper.
• Alpha particles would be stoppe. Gamma would go straight through.

Gamma Sources

•  Tracers in medicine. Source is injected or swallowed by patient. Progress around the body is monitored by detector. The source shold have a half-life of a few hours so that the patient is not exposed to unnecessary radiation.

Radioactive Dating - Used to find the age of ancient material. Carbon dating - wood and organic material. Uranium dating - age of igneous rocks.

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Energy from the Nucleus - 7.1 Nuclear Fission

Nuclear Fission - The splitting of an atomic nucleus. It is a chain reaction.

Uranium-235 or Plutonium-239 (the most common fissionable materials on Earth) must absorb one extra neutron. This causes them to break into two smaller nuclei and emmit 2-3 neutron, and energy is released. The energy released here is much greater than the energy released in a chemical process e.g burning. Becuase it is a chain reaction, it continues to go on.

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Energy from the Nucleus - 7.2 Nuclear Fusion

Nuclear Fusion - The process of forcing two Nuclei close enough together so that they form a                                single larger nucleus. Energy is released. It can be brought about using high                                speed. This is the process in which energy is released from stars.

Issues

• Nuclei approaching each other will repel each other due to their positive charge.
• So high temperatures must be used to help them overcome their forces and fuse.
• Because of these temperatures, the reaction cannot take place in a normal container but can be done by neing contained in a magnetic field.
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Energy from the Nucleus - 7.3 Nuclear Issues

• Background radiation major source is Radon Gas. This emits alpha particles so is a hazard to humans. It seeps through the ground from radioactive substances in rocks deep underground.
• Other sources are - cosmic rays, food and drink, air travel and nuclear weapons testing
• Medical sources (e.g x-rays) have an ionising effect. Radioactive substances also.
• Uranium and 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.
• To reduce nuclear radiation exposure workers should -

- keep as far away as possible from sources of radiation

- spend as little time exposed as possible

- shield themselves with concrete and lead.

THIS LAST BIT HAS BEEN A SLOG TO READ THROUGH. TAKE A BREAK. :)

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Energy from the Nucleus - 7.3 Nuclear Issues

• Background radiation major source is Radon Gas. This emits alpha particles so is a hazard to humans. It seeps through the ground from radioactive substances in rocks deep underground.
• Other sources are - cosmic rays, food and drink, air travel and nuclear weapons testing
• Medical sources (e.g x-rays) have an ionising effect. Radioactive substances also.
• Uranium and 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.
• To reduce nuclear radiation exposure workers should -

- keep as far away as possible from sources of radiation

- spend as little time exposed as possible

- shield themselves with concrete and lead.

THIS LAST BIT HAS BEEN A SLOG TO READ THROUGH. TAKE A BREAK. :)

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Energy from the Nucleus - 7.4 The Early Universe

Universe began with the Big Bang 13 billion years ago (scientist say). Firstly it was a hot glowing ball of radiation. In the first few minutes, the nuclei of the lightest elements formed. As the universe expanded over millions of years the temperature fell. Uncharged atoms were formed.

Before galaxies and stars formed, the universe was a dark, patchy cloud of hydrogen and helium. Eventually dust and gas were pulled to gether by gravitational attraction to form stars. The resulting intense heat started off nuclear fusion reactions in the stars causing them to give off light.

Large group of stars - Galaxies. We are in the Milky Way

Galaxy - a collection of billions of stars held together by their own gravity. Most of the universe is empty space.

Most of this you already knew anyway.

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Physics Module 2

Energy from the Nucleus - 7.5 The Life History of a Star

1) Protostar - Gravitational attraction pulles dust and gases together.

2) Star and Main Sequence Star - The protostar becomes denser, and hydrogen nuclei and other light elements go through nuclear fusion. Energy is released. Star core gets hotter and brighte.r Stars radiate energy from core. This stage can continue for billions of years until the star runs out of hydrogen nuclei. The star is stable because the inward force of gravity is balanced by the outward force of radiation from the core and is called a main sequence star.

3) Red Giant - The star cools down due to lack of hydrogen nuclei. Low mass become red giants. Helium and other light elements fuse to form heavier elements. Fusion stops and a white dwarf is formed. Eventually no more light is emitted and it forms a black dwarf.

Optional 3) Red Supergiant - Swell to become a red supergiant which continues to collapse. Eventually explodes in a supernova. The outer layers go into space. Neutron star (the core) is left. If this has a high enough mass this will forma black hole. The gravitational field of this is so stong not oven light can escape it.

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Physics Module 2

Energy from the Nucleus - 7.6 How the Chemical Elements are Formed

• Formed by fusion processes in the stars. Should we leave it at that? Lighter elemetns nuclei fuse to form heavier elements.This releases large amounts of energy.
• Anything 'heavier' than Iron will only be formed in the final few stages of a big stars life. This is due to the high amount of energy needed to fuse. The supernova causes the elements to get distributed.
• The presence of heavier elements in the Sun and inner planets is evidence that they were scattered by a supernova.

LOOK AT THE DIAGRAMS ON p71-72 FOR THIS AND THE PREVIOUS CARD!!!!!

YOU FINISHED MODULE 2 OF PHYSICS YOU BRILLIANT PERSON!!!!!!!

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