Download Core Science Revision – Physics

ELECTRICAL ENERGY
There are different types of energy –
 ELECTRICAL – flow of electric charge around a circuit
 EM WAVE – different waves from EM Spectrum
 SOUND – vibrations passed between atoms in a material
 HEAT – kinetic and elastic potential energy of molecules and atoms
 KINETIC – energy due to an object’s speed
 GRAVITATIONAL POTENTIAL – energy due to height above ground
 ELASTIC POTENTIAL – energy in stretched or compressed material
 CHEMICAL – energy stored in bonds between atoms
 NUCLEAR – energy stored in nucleus of atom
ENERGY CAN NEVER BE CREATED OR DESTROYED – IT CAN ONLY BE
CHANGED INTO A DIFFERENT FORM !
This means that there are many ENERGY TRANSFERS……
 ELECTRICITY is the most useful form of energy – it can be converted
into the main types of USEFUL ENERGY – HEAT, LIGHT, SOUND
and KINETIC.
EFFICIENCY  ENERGY is only USEFUL when it is converted to the form we want.
Energy transfers involve some losses – usually as HEAT or SOUND.
The rest of the energy is not useful and is WASTED.
 EFFICIENCY measures the proportion of energy that is USEFUL.
ENERGY EFFICIENCY = USEFUL OUTPUT ENERGY X 100
INPUT ENERGY
POWER –
 POWER is the amount of ENERGY transferred each SECOND. It is
measured in WATTS. 1 Watt = 1 Joule per second.
POWER = ENERGY TRANSFERRED
TIME

POWER of an appliance depends on its working VOLTAGE and the
CURRENT flowing through it.
POWER = VOLTAGE x CURRENT
ELECTRICAL UNITS AND COST  Electricity is sold in large units called the KILOWATT-HOUR (kWh).
The amount of electricity used depends on the POWER of the
appliance and HOW LONG it is used for.
NUMBER OF UNITS (kWh) = POWER x TIME

COST depends on the UNITS of electricity used and the COST PER
UNIT.
COST = NUMBER OF UNITS x COST PER UNIT
GENERATING + DISTRIBUTING ELECTRICAL ENERGY
ENERGY RESOURCES  NON-RENEWABLE sources will run out one day – they damage the
environment – but still provide most of our energy.
 RENEWABLE sources will not run out – they do less damage to the
environment – but don’t provide as much energy.
We need to become more EFFICIENT and ECONOMICAL in the use of nonrenewable FOSSIL FUELS (COAL, OIL, GAS) – AND – use renewable
sources such as SOLAR, WAVE, TIDAL, HYDROELECTRIC, WIND,
GEOTHERMAL and BIOMASS instead. NUCLEAR is also classed as NONRENEWABLE.
POWER STATIONS  POWER STATIONS use NON-RENEWABLE sources of energy –
FUEL is burnt to produce HEAT, which makes STEAM in a BOILER.
The STEAM drives a TURBINE, which turns a GENERATOR to make
ELECTRICITY. This allows CHEMICAL ENERGY (in fuel) to be
converted to HEAT ENERGY (steam), which is transferred to
KINETIC ENERGY (turbine), which is then transferred to
ELECTRICAL ENERGY (generator).
 HOWEVER – Burning FOSSIL FUELS releases CARBON DIOXIDE,
which adds to the GREENHOUSE EFFECT causing GLOBAL
WARMING. Burning coal and oil releases SULPHUR DIOXIDE, which
causes ACID RAIN. Using fossil fuels also cause other environmental
problems – like mining and spillages.
 NUCLEAR fuel is also used to produce heat in a boiler, which makes
steam to drive turbines. Nuclear power stations are very EXPENSIVE
to build and carry the risk of a major disaster like CHERNOBYL.
Nuclear waste is dangerous and difficult to dispose of.
RENEWABLES  SOLAR – solar cells generate electricity direct from sunlight. Good
choice in remote areas. Solar panels heat water pipes. Solar furnaces
create high temperatures to change water to steam to drive turbines.
No pollution and reliable when sunny.
 WAVE – Up and down motion of a wave drives a generator. No pollution
but spoil the view and can be a shipping hazard. Unreliable as waves
get smaller when wind drops.
 TIDAL – Big dams with turbines built across estuaries. Tide fills
estuary as it comes in. On the way out, the tide flows through
turbines and generates electricity. No pollution but spoil view, stop
ships and change habitats.
 HYDROELECTRIC – Flood a valley by building a dam. Water is
directed through a turbine to generate electricity. No pollution but
HUGE environmental impact – with loss of homes and habitats. Does
provide IMMEDIATE response to change in demand.



WIND – ‘Windmills’ put in exposed places. Wind turns turbine to drive
generator. No pollution, but spoil view and don’t work when the wind
drops.
GEOTHERMAL – Underground hot rocks are close to the surface.
Water pumped down, turned to steam and used to drive generator.
Very few places where this is available. Big cost to drill down.
BIOMASS – Fast growing trees are harvested and burned as fuel in a
power station. Need lots of land to grow trees.
NATIONAL GRID  The NATIONAL GRID is a NETWORK of pylons and power lines
which DISTRIBUTES electricity around the country from POWER
STATION to CONSUMER.
 To reduce ENERGY LOSSES from the HEATING effect of the
CURRENT, TRANSFORMERS are used.
 A STEP-UP TRANSFORMER INCREASES the VOLTAGE on the grid
to REDUCE the CURRENT flowing. A STEP-DOWN TRANSFORMER
then REDUCES the VOLTAGE to a SAFE level for consumers.
TRANSFORMERS  A TRANSFORMER changes VOLTAGE. The size of the voltage on the
SECONDARY side, depends on the VOLTAGE SUPPLIED on the
PRIMARY and the NUMBER OF TURNS of wire on both sides.
 STEP-UP TRANSFORMERS have more TURNS on the SECONDARY
and INCREASE the VOLTAGE (REDUCING the CURRENT).
 STEP-DOWN TRANSFORMERS have less TURNS on the
SECONDARY and DECREASE the VOLTAGE (INCREASING the
CURRENT).
HEAT TRANSFER AND DOMESTIC HEATING
There are three mechanisms of transferring HEAT ENERGY from a HOT to
COLD region CONDUCTION  Heat transfer within a SOLID.
 Two methods of conduction – VIBRATIONS passed between ATOMS
within the material due to the bonds between atoms (slow process) –

and – the movement of FREE ELECTRONS carrying THERMAL
ENERGY through the material.
METALS are GOOD conductors because they have many free
electrons. INSULATORS have very few free electrons.
CONVECTION –
 Heat transfer in LIQUIDS and GASES.
 Heating a liquid or gas causes the atoms to move FURTHER APART
and become LESS DENSE. Less dense fluids RISE and more dense
fluids FALL, setting up a CONVECTION CURRENT, which circulates
the heat.
RADIATION  All bodies emit radiation. The HOTTER the body, the MORE ENERGY
is radiated.
 Radiation is an ELECTROMAGNETIC WAVE, which doesn’t need
PARTICLES to transfer energy, so it can take place in a VACUUM.
 The surface of the object affects the amount of radiated heat
emitted or absorbed.
 DULL BLACK surfaces are very good EMITTERS of heat radiation.
SMOOTH, SHINY surfaces are very poor emitters.
 DULL BLACK surfaces are very good ABSORBERS of heat
radiation. SMOOTH, SHINY surfaces are very poor absorbers –
they REFLECT radiated heat.
VACUUM –
 Prevents conduction because there are NO ATOMS to pass on
vibrations and NO FREE ELECTRONS to move.
 Prevents convection because there are NO ATOMS to circulate and
form convection currents.
 Infra-red waves CAN travel through a vacuum as they don’t need
atoms in order to travel.
REDUCING HEAT LOSS There are different ways of minimising heat transfer to stop wasting
energy. Buildings use –
 CAVITY WALL INSULATION
 LOFT INSULATION
 DOUBLE GLAZING
 DRAFT PROOFING
 HOT WATER TANK JACKETS
These all attempt to TRAP AIR. This stops CONDUCTION, because air is a
good insulator, and stops CONVECTION because the air cannot move.

The COST-EFFECTIVENESS of each method depends on the
INSTALLATION COSTS, and how much MONEY is SAVED EACH
YEAR. This is assessed by calculating PAYBACK TIME.
PAYBACK TIME = TOTAL COST OF INSTALLATION
ANNUAL SAVING
THE CHARACTERISTIC OF WAVES
All waves are caused by VIBRATIONS. They have certain features –
 The AMPLITUDE measures the height of the wave from the MIDDLE
LINE to a PEAK.
 The WAVELENGTH covers a FULL CYCLE of the wave (from ONE
PEAK to the NEXT).
 FREQUENCY describes how many COMPLETE WAVES there are
every SECOND. It is measured in Hertz (HZ).
YOU MUST BE ABLE TO LABEL A DIAGRAM OF A WAVE AND
USE IT TO WORK OUT AMPLITUDE AND WAVELENGTH !


SOUND WAVES are LONGITUDINAL – the DIRECTION of the
DISTURBANCE creating the wave is in the SAME DIRECTION the
wave travels.
LIGHT WAVES are TRANSVERSE – the DIRECTION of the
DISTURBANCE creating the wave is at RIGHT ANGLES to the wave
travel.
WAVE EQUATIONS There are 2 equations for WAVE SPEED –
SPEED = DISTANCE
TIME
SPEED = FREQUENCY X WAVELENGTH
THE EM SPECTRUM AND ITS USES
The ELECTROMAGNETIC SPECTRUM contains SEVEN types of wave. All
the waves travel at EXACTLY the SPEED of LIGHT (in a VACUUM) 
RADIO WAVES

MICRO WAVES
LONG WAVELENGTH
LOW FREQUENCY

INFRA RED

VISIBLE LIGHT

ULTRA VIOLET

X – RAYS
SHORT WAVELENGTH HIGH FREQUENCY

GAMMA RAYS
YOU MUST BE ABLE TO LABEL A DIAGRAM OF THE EM SPECTRUM !
The ENERGY of the EM wave changes with the FREQUENCY of the wave.
The HIGHER the frequency, the greater the energy, and the more
DANGEROUS.
We see VISIBLE LIGHT. Other parts of the EM SPECTRUM are used for
different things  RADIO WAVES are used for COMMUNICATION. TV and FM Radio use
a short wavelength (1 M). Long wave radio has a wavelength of 1 KM.
 MICROWAVES are used for COOKING and also for COMMUNICATION
with SATELLITES. Water absorbs microwave energy and converts it to
heat.
 INFRA RED is the same as HEAT RADIATION – given out by all HOT
GLOWING objects such as grills, toasters, etc... Infra red is also used
for NIGHT VISION, REMOTE CONTROLS, and COMMUNICATION in
fibre optic cables..
 ULTRA VIOLET LIGHT causes TANS, and potentially SKIN CANCER.
It is also used for SECURITY MARKING.
 X-RAYS are used to spot BROKEN BONES. They pass easily through
flesh but are absorbed by the MORE DENSE bone. X-RAYS can cause
CANCER, so medical staff take PRECAUTIONS - LEAD SCREENS,
LEAVE the ROOM, keep EXPOSURE to a MINIMUM.
 GAMMA RAYS are used to TREAT CANCER. Also to KILL BACTERIA to
STERILISE MEDICAL EQUIPMENT, or KEEP FOOD FRESH. You must
take the same precautions as for X-Rays.
EM Waves can be REFLECTED and REFRACTED.
REFLECTION –
 Reflection of LIGHT allows us to see objects.
 If light shines on an UNEVEN SURFACE, it reflects at DIFFERENT
ANGLES. This is called DIFFUSE REFLECTION.
 If light reflects from an EVEN SURFACE (SMOOTH and SHINY), it
is all reflected at the SAME ANGLE. This is called CLEAR
REFLECTION.
The LAW OF REFLECTION ANGLE of INCIDENCE = ANGLE of REFLECTION
REFRACTION  Waves CHANGE SPEED as they move from one medium into another.
 The change in speed causes a CHANGE IN DIRECTION.
 WAVELENGTH also changes.
Waves SLOW DOWN when they move into a MORE DENSE medium.
This causes them to refract (bend) TOWARDS the NORMAL. Waves
SPEED UP when they move into a LESS DENSE medium, and refract
(bend) AWAY from NORMAL.
TOTAL INTERNAL REFLECTION happens when a ray of light travelling
through a dense material, has an ANGLE OF INCIDENCE that is GREATER
than the CRITICAL ANGLE of that material.
OPTICAL FIBRES  OPTICAL FIBRES carry information using total internal reflection.
They trap the light y ensuring that it enters the fibre at an angle
greater than the critical angle.
 They have many advantages over traditional copper cables – FASTER
COMMUNICATION, very efficient with LITTLE ENERGY LOSS,
LITTLE ENVIRONMENTAL INTERFERENCE, very SECURE –
however they are still EXPENSIVE and must be PRECISELY
INSTALLED.
TELECOMMUNICATIONS –
 Microwaves can be used to COMMUNICATE over long distances using
MOBILE PHONES and SATELLITE LINKS.
 Infra-red waves are used for INTERCONTINENTAL OPTICAL
FIBRES.
HEALTH RISKS  High power mobile phone transmitters and tetra masts emit
ELECTRIC and MAGNETIC FIELDS, which may be DANGEROUS to
nearby residents.
 EVIDENCE is ANECDOTAL – DIZZINESS, NAUSEA, CANCER ! –
but the evidence is not always IMPARTIAL.
YOU MUST BE ABLE TO DRAW DIAGRAMS TO SHOW REFLECTION.
REFRACTION AND TOTAL INTERNAL REFLECTION !
SOLAR SYSTEM
The Sun is at the centre of our solar system. The planets move around the
sun in ELLIPTICAL ORBITS in the SAME DIRECTION.
FORMATION OF THE SOLAR SYSTEM  A cloud of HYDROGEN gas and DUST collected together and
collapsed due to GRAVITY to form our SUN.
 The cloud rotated, converting GRAVITATIONAL POTENTIAL
ENERGY to KINETIC ENERGY to HEAT ENERGY as the particles
MOVED and COLLIDED.
 A DENSE central core called a PROTOSTAR formed, surrounded by a
thin disc of material. NUCLEAR REACTIONS in the protostar
converted HYDROGEN to HELIUM.
 GRAVITY caused large particles to collect together forming
PLANETECIMALS, a few KM across. These continued to collide and
formed PLANETS.
 The inner planets had too many COLLISIONS to form large planets.
These four planets – MERCURY, VENUS, EARTH and MARS – are
ROCKY and were pulled CLOSER to the sun.
 Four very large planets – JUPITER, SATURN, URANUS and
NEPTUNE formed from GAS further out in the solar system.
ASTEROIDS –
 There is an ASTEROID BELT between Mars and Jupiter containing
THOUSANDS of asteroids.
 Asteroids are lumps of rock ranging up to 100s OF KMs across and
could be the remains of a smashed planet or moon.
 The asteroids are kept in orbit by the force of GRAVITY due to
JUPITER.
COMETS –
 Comets have very ELLIPTICAL ORBITS with the sun at ONE END.
They pass well OUTSIDE our solar system – this is why they only
appear every few years. Gravity SPEEDS UP the comet as it gets
NEAR to the sun, and SLOWS it down as it gets FURTHER AWAY.
 Comets are balls of ROCK and ICE. RADIATION PRESSURE from
the sun melts the ice, which forms the TAIL of the comet. This means
the tail will always points away from the sun.
GRAVITY  GRAVITY is the FORCE of ATTRACTION between all bodies in the
Universe.
 The force of gravity INCREASES with MASS and DECREASES with
DISTANCE. A SMALLER BODY will orbit around a LARGER BODY
because of GRAVITY, and because of its HIGH SPEED.
SATELLITES  SATELLITES can be NATURAL or MAN-MADE.
 The MOON is a NATURAL SATELLITE of the EARTH.
 MAN-MADE SATELLITES can be GEOSTATIONARY or POLARORBITING.
 GEOSTATIONARY SATELLITES are used for COMMUNICATION.
They have a HIGH ORBIT over the EQUATOR, and stay above the
SAME POINT above the earth. They orbit at the same speed as the
earth – once every 24 HOURS.
 POLAR ORBITING SATELLITES are used for MONITORING
WEATHER or SURVEILLANCE. They have a LOW ORBIT and pass
over the NORTH and SOUTH POLES. They orbit the earth every
many times a day.
DISCOVERIES  Early theories suggested that all heavenly bodies orbited around the
Earth – the GEOCENTRIC model. However, observations by Galileo
(with his newly invented telescope) concluded that the planets orbited
around the sun – the HELIOCENTRIC model.
 Modern telescopes linked to computers look for movements in the
solar system by taking pictures of an area of night sky at REGULAR
INTERVALS and analysing the pictures for DIFFERENCES. The
SIZE, SPEED and DIRECTION of travel can indicate the type of
body moving.
STARS
SUN’S SOURCE OF ENERGY  Early theories suggested that the Sun’s energy came from BURNING
COAL (chemical energy) or from COMETS FALLING (gravitational
potential energy). These theories suggested that the Sun was
relatively young.
 The theories were dismissed when geologists discovered that the
Earth was HUNDREDS OF MILLIONS of years old, and DARWIN
proposed his theory of EVOLUTION.
STARLIGHT –
 White light can be split into a CONTINUOUS SPECTRUM with no
gaps.
 If white light is passed through a GAS CLOUD before being split, the
gas ABSORBS some of the colours in the spectrum. This
ABSORPTION SPECTRUM has BLACK LINES where particular
colours have been absorbed by the gas.
 The position of the BLACK LINES (ABSORPTION LINES) on the
absorption spectra, changes with the gas used.
 We can identify different gases from the pattern of the lines.
 From this we know that the SUN is mostly made of HYDROGEN and
HELIUM, but also contains small amounts of other elements.
 The BRIGHTNESS of the colours on the absorption spectra also tells
us the TEMPERATURE of the surface of the sun.
NUCLEAR FUSION IN STARS –
 The Sun is a ball of hot gas, 76% HYDROGEN (by mass) and the rest
mostly HELIUM.
 The temperature of the CORE is at 15 MILLION degrees, which
allows NUCLEAR FUSION to take place. HYDROGEN NUCLEI
(PROTONS) fuse together to form HELIUM NUCLEI, releasing
ENERGY.
 The energy RADIATES outwards from the core and is CONVECTED
to the SURFACE by circular currents of gas. The surface of the sun is
approximately 6000  C
 SOLAR FLARES blast particles out from the surface of the sun as
the SOLAR WIND, which reaches the Earth.
 The Earth’s MAGNETIC FIELD protects us from the solar wind,
funnelling the gas particles at the POLES.
 Our sun is approximately halfway through it’s 10 BILLION YEAR
lifespan.
LIFECYCLE OF STARS  Stars form from CLOUDS of DUST and GAS, which COLLAPSE
together due to GRAVITY. The gas mostly consists of HYDROGEN.
 As the gas cloud collapses, it becomes more DENSE and starts
ROTATING. The gas/dust particles move together, transferring
KINETIC ENERGY to HEAT ENERGY as they COLLIDE. This causes
an INCREASE in TEMPERATURE, which forms a HOT BALL of gas
called a PROTOSTAR at the centre.
 Once the temperature is high enough (15 million degrees), NUCLEAR
FUSION converts HYDROGEN to HELIUM, which gives out HEAT
and LIGHT.
 The star is now in its STABLE PERIOD, where the OUTWARD
PRESSURE due to the gas and EM RADIATION, BALANCES the
INWARD FORCE of GRAVITY. The star is now called a MAIN
SEQUENCE STAR – our sun is in the middle of this period and is 5
BILLION YEARS OLD.
 Eventually the hydrogen RUNS OUT and the star EXPANDS, as
HELIUM is FUSED into HEAVIER NUCLEI, releasing even more
energy.
 Stars the size of our sun swell to become a RED GIANT. Outer
layers are blown into space leaving a PLANETARY NEBULA.
It’s core then shrinks and cools to a WHITE DWARF and
finally a BLACK DWARF once all fuel runs out.

BIG stars have further NUCLEAR REACTIONS using heavier
elements and expand to a RED SUPERGIANT. Fuel is quickly
used up and the core suddenly collapses and then throws outer
layers into space in a SUPERNOVA explosion. The DUST and
GAS thrown into SPACE is used in the formation of new stars.
The central core that remains is called a NEUTRON STAR. If
the star was really MASSIVE, the neutron star continues to
shrink and eventually turns into a BLACK HOLE.
THE UNIVERSE
Our SUN is one of about ONE HUNDRED THOUSAND MILLION stars in
our GALAXY. Our Galaxy is a SPIRAL GALAXY called the MILKY WAY, and
is one of a BILLION galaxies in the UNIVERSE.
RED SHIFT –
 Light can be split into a CONTINUOUS SPECTRUM from RED to
VIOLET.
 The RED end of the spectrum has the LONGER WAVELENGTH and
LOWER FREQUENCY. The VIOLET (BLUE) end of the spectrum has
the SHORTER WAVELENGTH and HIGHER FREQUENCY.
 Light emitted from a MOVING SOURCE changes WAVELENGTH and
FREQUENCY. This is noticeable for VERY FAST moving objects.
 If the light source is moving TOWARDS us, the wavelength gets
SHORTER and the frequency gets HIGHER. We say light has been
shifted to the BLUE end of the spectrum.
 If the light source is moving AWAY FROM us, the wavelength gets
LONGER and the frequency gets LOWER. We say light has been
shifted to the RED end of the spectrum.
 Light emitted by distant galaxies has ABSORPTION LINES indicating
the presence of HYDROGEN and other gases. The absorption lines
SHIFT different amounts toward the RED end of the spectrum for
different galaxies.
 This RED SHIFT suggests that all galaxies are MOVING AWAY from
us. The amount of RED SHIFT tells us how FAST the galaxy is moving
– the GREATER the SHIFT, the GREATER the SPEED.
EXPANDING UNIVERSE AND THE BIG BANG –
 As all galaxies show a red shift, they must all be moving away from
each other. More DISTANT galaxies have a LARGER red shift, and so
are moving away FASTER.
 As all galaxies are moving apart, this suggests that the UNIVERSE is
EXPANDING.
 At some point in time, all MATTER must have started at a COMMON
POINT in space.
 Astronomers think that the Universe started with a huge explosion
called the BIG BANG, approximately 12 BILLION years ago.