Physics Revision

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  • Created by: Harry
  • Created on: 19-11-12 20:16

Continued....

Payback Time= cost of insulation DIVIDED BY Savings per year

Specific Heat Capacity- It is the capacity for a substance to take up heat energy with a small increase in temperature. The higher the SHC, the lower the temp increase

Joules= kg X SHC x Temp riseEnergy Efficient Homes- To be energy efficient, we need to use as much energy as possible for the desired purpose. The key is to have good insulation. To do this effectively, we must reduce the amount of ways energy can escape.

We can install:  

  • Double Glazed Windows
  • Rubber draught blockers
  • Glass fibre insulatin wool between brick layers to stop convection currents.
  • Loft insulation-Reflective foil reflects radiation and traps a thick layer of air.

REMEMBER: Thermal Radiation is the transfer of energy by infra-red waves (read more in the electromagnetic spectrum section).

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Generating Electricity

Non- Renewable Resources

A non-renewable resource is one that effectively cannot be replaced once it has been used like fossil fuels, (coal, oil and gas).

The combustion of fossil fuels causes environmental impacts due to the release of carbon dioxide (greenhouse gas).

A greenhouse gas traps the sun's heat inside the Earth's atmosphere causing global warming. 

Many fossil fuels also contain sulphur, so when they combust, sulphur dioxide forms causing acid rain which can cause damage to plants and buildings etc. 

Renewable Resources

A renewable energy resource is one that will not run out and can be used multiple times such as geothermal energy, wave energy, solar energy, wind energy and hydroelectricity (READ TEXTBOOK FOR DETAILS).

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Electricity and Nuclear Energy

Nuclear Energy

Nuclear reactors use uranium to produce energy, a particular isotope is needed. 

Advantages: can be clean and cause little damage to environment

Disadvantages: Risk of Nuclear accidents

                        Cost per Unit of electricity is very low.

                        Power stations expensive to build.

Electricity

IS NOT AN ENERGY RESOURCE

Electricty is generated by resources.

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Waves and Electromagnetic Spectrum

Process-

Stored energy in the form of fossil fuels is used to heat water

Heat energy in high pressured steam drives turbines

The movement energy of the rotating turbines spins a generator

Leading to an electrical energy output.

Frequency=Hertz

A frequency is how many wavelengths pass a point in 1 second

E.g. 20 wavelengths in 2 secs= 10 Hertz

EQUATION- Frequency (Hertz)= 1 DIVIDED BY Time (Seconds)

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Continued....

Only in a vacuum do all wavelengths travel at the same speed (3 x 10 to the power of 8)

Speed of a wave (metres per second) = Frequency (Hertz)  x Wavelength (Metres)

Smaller the wavelength, the higher the frequency

WHAT ARE WAVES?

Waves are a means of transferring energy from place to place.

These can travel in longitudal or transverse waves.

DESCRIBING WAVES

Amplitude- The maximum movement of particles from their resting position cause by a wave.

Wavelength- The distance between a particular point on a wave and the same point on the next wave.

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Electromagnetic Spectrum

The electromagnetic spectrum.All the waves have the following properties:

  • They all transfer energy 
  • They are all transverse waves 
  • They all travel at the speed of light in a vacuum
  •  They can all be reflected, refracted and diffracted.

The further to the right of the electromagnetic spectrum, the frequency increases but the wavelength decreases.

Radio Waves-

  • given out by transmitter
  • used for communications

Microwaves-

  • Communications, cooking food and radar are uses
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Continued....

Infra-red-

  • The hotter the object, the more energy emitted as infra-red

Visible Light-

  • Visible to human eye
  • Sent along optical fibres for communication
  • When refracted, the white light is split into the colours of the rainbow
  • Red has longest wavelength and lowest frequency
  • ROYGBIV

UV-

  • Harmful to eyes and skin
  • UV lamps and the sun

X-rays-

  • Pass easily through soft body tissue-overexposure can lead to cancer
  • Used to check the internal structure of objects such as security procedure at airports
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Continued....AND Communications Using Waves

Gamma Rays- 

  • Highly penetrating rays which cause damage to cells
  • Cause mutations in genes, as well as cancer.
  • Kill micro organisms and sterilisation of medical instruments.

Communications Using Waves

Two types of wave- analogue and digital

Digital- Information is converted into a sequence of numbers (binary, 0 and 1). These codes are then converted into a series of electrical impulses which are sent down telephone lines.

Advantages- Regeneration of digital singlas are clean and accurate. Regeneration of analogue signals includes any background noise.

Analogue- A series of waves that varies continuosly in amplitude or frequency between zero and a maximum value.

THE HIGHER THE FREQUENCY, THE LARGER THE AMOUNT OF INFORMATION CARRIED

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Radioactive Decay and Half Life

              Relative Mass of Particle         Relative Charge of Particle

Electron                1                                         -1

Proton                 2000                                     +1

Neutron               2000                                      0

Mass Number= Neutron Number + Proton Number (total nucleons)

Atomic Number- Proton Number

Isotopes- Isotopes of the same element have the same proton number but a different neutron number. SAME ATOMIC NUMBER, DIFFERENT MASS NUMBER

The stability of an isotope depends on the neutron number. Too many or too few can destabilise the atom.

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Continued....

Ionising Radiation- When an unstable nuclei decay, they give out ionising radiation (causes atoms to lose of gain electric charge, forming ions). 

There are three types of ionsing radiation: Alpha, Beta and Gamma

Alpha- 

  • Fast moving particles
  • Helium nuclei-without orbiting electrons
  • Loses an electron, becoming positively charged
  • Large mass, made up of four nucleons (mass number 4) and have a charge of +2.
  • Short range- interaction with atoms along their paths
  • Can only travel though a few centimetres of air and cannot penetrate a few milimetres of paper.

Beta-

  • Very fast moving
  • Ejected by decaying nucleus
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Continued....

  • The stability of a nucleus depends on the proportion of protons to neutrons.
  • NEUTRON IN THE NUCLEUS SPLITS TO FORM A PROTON AND ELECTRON
  • Proton remains in nucleus
  • Electron is ehected at high speed as a beta particle
  • Relative charge of -1
  • Lighter than Alpha
  • Interact with matter in their paths less frequently than alpha particles because they are smaller and carry less charge.
  • Travel further than alpha particles and pass through paper easily and only absorbed by denser materials like aluminium.

Gamma Rays-

  • Electromagnetic Waves with short wavelengths
  • No mass and no charge
  • Weakly ionising and interact occasionally with atoms in their paths.
  • Extremely penetrating and pass through all par the densest materials with ease. 
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Continued....

Alpha Decay

-4 to the mass number

-2 to the atomic number

Beta Decay

Don't do anything to mass number

-1 to the atomic number

Gamma Decay

 NO change to the mass number or the atomic number

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Half Life

Background Radiation- Ground and Buildings, Cosmic Rays, Medical, Nuclear Power, Radon Gas, Food and Drink

HALF LIFE- The half life of a radioactive sample is the average time taken for half the original mass of the sample to decay. The half-life is different for different radioactive isotopes.

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BIG BANG

Red shift- Wavelength gets bigger if the galaxies move away faster than the speed of light. EXPANDING UNIVERSE- supports the idea

Blue shift- The galaxies contract if galaxies moves towards us. 

Cosmic Microwave Background- The relatively uniform background radiation is the remains of energy created just after the Big Bang.

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Hooke's Law

An object behaves elastically if it returns to its original shape and size once a force has been removed.

The extension is directly propetional to the load applied, provided the kimit of proportional is not exceeded.

If exceeded, the object will not reutn to its original size and shape.

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Energy

Energy can not be destroyed but only transferred.

(IR)Radio Waves------ROYGBIV------X rays (UV)

Thermal Energy is trapped by: 1) Colour: White reflects and Black absorbs 

2) Texture: Gloss reflects and Matt surfaces trap.

Conduction occurs as the metal has free electrons between particles meaning energy can be transferred through out the metal through collisions between electrons and partciles.

Convection is the transfer of heat through fluids by the upward movement of warmer, less dense regions of fluid through convection currents. 

Energy Diagrams: Sankey diagrams are simple and clear. The energy flow is represented by arrows whose width is proportional to the amount of energy lost.

Efficiency=                                                  Useful energy output from the system                                                                                ---------------------------------------                                                                                  Total Energy Input to the System

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Distance/Time Graphs, Acceleration

Speed = Distance / Time

Speed and velocity are different. Velocity, the direction is given as well.

Acceleration

Acceleration = change in velocity / time taken

a = v-u / t

Unit= m/s ^2 

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Forces

When forces are balanced, there is no acceleration, when forces acting on a vehicle are unbalanced, the vehicle will accelerate.

The reaction force is equal and opposite of the one of the weight force.

Reaction and weight always balance but if the driving force is more than friction, it will accelerate.

RESULTANT FORCE

If there are a number of forces acting on a body, they may be replaced by a single force which produces the same effect- the resultant force.

FORCE AND ACCELERATION

Doubling the force, doubles the acceleration

Doubling the mass for a constant force, halves the acceleration

EQUATION- Force (N)= Mass (kg) x Acceleration (m/s ^2)

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On the Road

Overall Stopping Distance= Thinking distance + Braking Distance

Thinking distance is the distance the vehicles travels during a reaction time. Factors that increase this are:

  • Drugs
  • Age
  • Alcohol
  • Illness
  • Tiredness

The Braking Distance is the distance it takes for the vehicle to stop after the brakes have been applied. Factors that increase this are:

  • Brake Quality
  • Wetness of roads
  • Worn Brakes
  • Quality of tyres
  • Mass of vehicle
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Weight and Mass

Mass is the amount of matter an object contains

Weight is the inwards force a plant exerts on an object

Weight is another name for gravitational force acting on something.

All masses in the universe attract each other, the close together they are then the greater the pull is between them.

EQUATION- Weight= Mass x Gravitational Field Strength

On Earth g= 10N/Kg

On the Moon g=1.6 N/Kg

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Terminal Velocity

Terminal velocity is reached when two forces balance out.

In the case of a sky diver, a terminal velocity is reached when weight and air resistance gradually balance out once the diver stops acceleratin meaning he has reached terminal velocity.

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Energy and Work, Power

Work is done when a force moves the object it acts upon. 

Work (Joules) = Force (N) x Distance (metres)

Power is the rate of doing work.

Power (Watts) = Work done (Joules) / Time taken (seconds)

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GPE and Kinetic Energy

GPE =mgh

mass x gravity x height

Measured in Joules

Kinetic Energy = 1/2mv^2

Kinetic energy is lost after a collision as energy will be converted into other energy types such as sound and heat.

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Momentum, Collisions

Momentum (kg m/s) = mass x velocity

The total momentum before a collision is equal to the total momentum after a collision provided there isn't an external force.

m1v1 +m2v2 = m1v1+ m2v2

Before                After

An elastic collision is where the total kinetic energy before the collision is equal to the total kinetic energy after the collision.

Force = change in momentum / time taken

Car safety features that increase the imapct time are:

  • Seatbealts-spreads the force over a larger area, impact decreases
  • Airbags
  • Crumple zones-force exerted by impact decreases
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Electrical Charge

Charge is measured in coulombs.

Like charges repel, unlike charges attract.

An uncharged object is atteacted by a charged object because the charges in the uncharged object rearrange.

When an object is rubbed with a duster, electrons are transferred either to or from the duster. When electrons transfer from the duster, the object becomes negatively charged and vice versa.

EARTHING- when the charge flows down to earth.

Electrical Current =Charge / Time

CURRENT IS MEASURED IN AMPS

TIME IN SECONDS

CHARGE IN COULOMBS 

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Resistance

Resistance in Ohms = Voltage / Current

Through a resistor, as the volts increase, the amps increase and so does the resistance.

In a LDR (Light Dependant Resistor), the greater the intensity of light, the lower the resistance.

Uses of a LDR: Light meter and a light swtich

In a thermistor, as the temperature increases, the resistance decreases and vice versa.

Uses of a thermistor: Greenhouses, Digital themometer, heat switch in central heating, oven, fridge, air conditioning

Resistance and the length of wires

As the length of the wire increases, so does its resistance.

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Diodes

The diode only conducts the current when the current is in the forward direction. In reverse, it blocks the current so results are equal to zero. This is because its forward resistance is extremely low, its reverse resistance is extremely high.

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Series and Parallel Circuits

SERIES

The Current is the same everywhere in the circuit.

The battery voltage is shared out between the compenents in a series circuit.

The total resistance in a series circuit = r1 + r2 + r3

PARALLEL

When the current reaches the junction, it splits three ways going to different parts of the circuit. I= I1+I2+I3

The voltage across each bulb is the same and is also the same as the battery voltage.  

V= V1=V2=V3

The greater the number of resistors in paralle, the lower is the overall resistance.

1/R = 1/ R1 + 1/R2 + 1/R3

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AC, Fuses and Electrical Power

In AC circuits, the current flows forwards and backwards at the frequency of the power supply. E.g. for UK mains, the frequency is 50 Hertz.

(http://www.google.co.uk/imgres?q=uk+mains+plug&num=10&hl=en&tbo=d&biw=1280&bih=738&tbm=isch&tbnid=z5e5g4YfJW_UZM:&imgrefurl=http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/electricity/mainselectrev1.shtml&docid=D16ZeL0o1Kz-oM&imgurl=http://www.bbc.co.uk/schools/gcsebitesize/science/images/68_wiring_a_plug.gif&w=226&h=254&ei=LzytUPLUKKmk0QXdiYDADw&zoom=1&iact=hc&vpx=263&vpy=147&dur=511&hovh=203&hovw=180&tx=144&ty=111&sig=117770205092346525589&page=1&tbnh=139&tbnw=123&start=0&ndsp=31&ved=1t:429,r:1,s:0,i:88)

The three standard fuse sizes are: 3 Amp, 5 Amp and 13 Amp.

When a current passes through a wire, a wire gets hot. If there is too much current, then the wire melts, breaking the circuit.

Fuse Calculations

Electicaly Power (Watts)= Voltage x Current

Resettable Fuses- Uses electomanet. When current is high enough, the electromagnet opens the swtich, breaking the circuit. 

Advantages, more pressure trip value and quick and easy to reset.

Earth leakage circuit breakers- Monitors current between live and earth. Even the smallest leakage current, trips the devide and breaks the current

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Electrical Energy and Charge

Energy (Joules)= Power x Time

Energy can also = charge x voltage

Energy= Current x Time x Voltage

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Discovery of the Nucleus

Sub atomic research involves firing high energy projectile particles at the target particle and carefully observing the outcome.

Plum Pudding model

By 1900, scientists knew that matter contained electons, protons and neutrons. 

Basically, an atom was considered to be a lump of positive material embedded with electrons.

Rutherford's Scattering Experiment-Fired alpha particles at gold atoms

Concluions were:

  • Most of the volume of the atom was empty space
  • All the positive charge and most of the mass is concentrated in a tiny central core
  • Negative electrons orbit the nucleus

Alpha particles deflect away as like charges repel and some deflect more as 1/8000 bounce back.

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Fission

Nuclear fission heappens when a uranium-235 nucleus is hit by a neutron and splits into two nuclei.

When the atom undergoes fission, it releases two or three neutrons and energy.

The energy is released in the form of gamma radiation and kinetic energy.

The fission neutrons may collide with other uranium-235 nuclei and produce a chain reaction.

Functions of:

Control Rods- Absorb the neutrons and slow down or stop reactions.

Moderator- Slow down fast moving neutrons from fuelrods

Coolant- Transform themral energy to the heat exchanger from the core.

DISADVANTAGES- Produces radiioactive products with long half lives and uranium needs to be mined

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Fusion

Nuclear fusion happens when two hydrogen nuclei collide at high speed to prevent repelling and fuse together to form a nucleus.

When nuclear fusion occurs, the energy is released in the process.

The colliding nuclei need to have enough kinetic energy to fuse, otherwise they will repel each other and not fuse.

A gas in a fusion reactor is heated by passing an electric current through it.

The gas becomes so hot it forms a plasma of small nuclei.

The plasma is contained using a magnetic field to prevent it from touching the container walls.

When hydrogen nuclei fuse, helium is formed as a product

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Density

Density = Mass / Volume

The units of density are : kg/m^3

                                      g/cm^3

Density of water= 1000 kg/m^3

The density of an object is its mass divided by its volume.

Hot air ballons are able to work due to the heated air is less dense than the air outside the ballon which is more dense meaning the balloon rises but also the average density of the hot air and balloon skin is less dense than the surroundings.

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Pressure

Pressure= Force / Area

Unit = N/m^2

IN SOLIDS

Pressure at a particular depth acts equally in all directions. 

Pressure acts inwards on an object placed inside the liquid.

 Pressure difference= height x density x gravity

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Gas Pressure

Atmospheric Pressure= 101 000 Pascals = 1 ATm

A manometer can be used to measure high pressures.

HOW DO GASES EXERT PRESSURE?

Gases consist of molecules which are in constant random motion. When the molecules hit the container walls, a small force is exerted. When lots of molecules collide, it causes a steady force causing a pressure.

BOYLE'S LAW

Gas molecules are in constant random motion shown by Brownian motion.

Boyle's Law= p1v1 = p2v2

p1v1 = p2v2

1x2=3v2

2/3 l

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Pressure Law and Absolute Zero

Pressure Law= p1/t1 = p2/t2

Absolute zero = -273 Degrees C or 0 K (Kelvins)

Temp in K = Temp in Degrees C + 273

Temp in Degrees C= Temp in K - 273

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Moments

The turning moment of a force is increased by either increasing the force or increasing the perpendicular distance from the pivot.

Turning Moment = Force x Perpendicular Distance

Moments are measured in Nm or Ncm

The law of moments

For an object in equilibrium, the otal of the clockwise moment is equal to the total of the anticlockwise moments.

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Centre of Gravity and Stability

Centre of Gravity= The centre of gravity is the point through which the weight force acts.If this is through a suspended object, the centre of gravity lies directly beneath the point of suspensions.

For irregular shaped objects, the experiment is the following:

Apparatus: Stand/ Clamp, Drawing Pin, Cork, Plumb Line, Object

  • Suspend object from one point
  • Draw a line along the path of the plumb line
  • Suspend shape from a second hole
  • Repeat the procedure
  • Draw lines of intersection to locate the centre of mass

Stability- An object will topple when the line of action of the weight lies outside of its base.

To make an object more stable, we can:

  • Lower the centre of gravity
  • Increase the size of the base
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Circular Motion

The magnitude of the velocity is constant but its direction changes, meaning the velocity keeps changing.

Since velocity is changing, the object must be accelerating, creating a resultant force.

If the mass increases or the radius decreases, the tension increases.

CENTRIPETAL FORCE ACTS TOWARDS THE CENTRE IN ALL CASES

Stable Orbit- For an orbit to be stable, the orbital speed must be exactly right for the particular height. If too slow, then the gravity pulls the object in a downward spiral. if spped is too high, then the object will be propelled into space

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Satelittes

                        Polar                                                        Geostationary

Height               Low                                                         High

Time of Orbit     2 hours                                                    4 hours

Uses                Photography, Data Collection, Maps          Communications and Navigation

EQUATION

Orbital Velocity= 2πr/T

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