Transcript Biology revision

P1 - Universal physics
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How science works
• Independent variable – this is the quantity that you
change
• Dependent variable - this is what you measure
• Control variable – this is what must be kept the
same to ensure a fair test
• Hypothesis – an idea based on observations without
experimental evidence
• Secondary evidence - data collected by someone
else, you may find it in a book or on the internet
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How do scientist validate results?
1. they repeat experiment results
2. they publish their findings in scientific journals
3. conference presentation
4. peer review/other scientists investigate the
same findings.
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Models of the solar system
• Geocentric model(Ptolemy) the earth at the centre and all
the planets and the sun orbiting
around it
• Heliocentric model(Nicolaus
Copernicus) - the sun at the
centre of the universe, based
on observations with the
telescope
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Observing the universe
• Optical telescopes observe visible
light from space
• The Hubble telescope is an optical
telescope in space
• Optical telescopes on the ground
have some disadvantages:
1. they can only be used at night
2. they cannot be used if the
weather is poor or cloudy.
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Observing the universe
• Many objects in space do not give out visible light but
give out other types of energy-carrying waves like
radio waves and microwaves
• The Planck space
telescope detects
microwaves
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Observing the universe
• Radio telescopes detect radio waves coming from
space, they are usually very large and expensive.
• Advantage over optical
telescopes –
1. can be used in bad weather
because the radio waves are not
blocked by clouds as they pass
through the atmosphere.
2. can also be used in the daytime
as well as at night.
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Telescopes
• Telescopes use mirrors and lenses to bend, magnify and
focus the light.
• Parallel light rays entering a convex lens come out and pass
through at a point known as the focal point
• Converging lenses are used in a refracting telescope
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Investigating converging lenses
• A Converging lens can be used to produce a magnified
image.
The amount of magnification depends on:
1. How curved the surface of the lens is
2. How far the object is from the lens
Two types of image can be seen.
1. A real image Is the image formed where the light rays
are focused.
2. A virtual image is one from which the light rays appear
to come, but don’t actually come from that image like
in a plane (flat) mirror.
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Investigating converging lenses
• Object more than two focal lengths from the lens
image is inverted, smaller, appear between 1 and 2
focal lengths, real image
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Investigating converging lenses
• Two focal lengths in front
image is inverted, same size, appears at 2 focal lengths,
real image
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Investigating converging lenses
• Between one and two focal lengths
image is inverted, made bigger, appear beyond 2 focal
lengths, real image
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Investigating converging lenses
• One focal length
no image is formed
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Investigating converging lenses
• Object is less than one focal length from the lens.
image right way up, image made bigger, virtual image
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Refracting telescopes
• A refracting telescope works by bending light through a
lens so that it forms an image
• Problems with refracting telescopes:
1. some of the light reflects off the lens so the image is
very faint
2. the size of the lens is limited
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Reflecting telescopes
• In a reflecting telescope the image is formed by
reflection from a curved mirror
• It is then magnified by a Convex lens (the eyepiece)
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Compare and contrast lenses and
mirrors
Similarities
1. A convex lens acts a lot like a concave
mirror.
Both converge parallel rays to a focal
point, and form images with similar
characteristics.
2. A concave lens acts a lot like a convex
mirror.
Both diverge parallel rays away from a
focal point, and form only virtual, smaller
images.
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Compare and contrast lenses and
mirrors
Differences
1. Light reflects from a mirror. Light goes through, and is
refracted by, a lens (with some light being reflected off
the lens).
2. Lenses have two focal points, one on either side of the
lens.
3. A concave mirror converges parallel light rays to a
focal point. For lenses, parallel rays converge to a point
for a convex lens. A convex mirror diverges light, as does
a concave lens.
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Refraction in different materials
Remember the word:
TAGAGA
Towards (normal)
Air
Glass
Away (from normal)
Glass
Air
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Effects of refraction
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Effects of refraction
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What are waves?
• Waves are vibrations that transfer energy from place
to place without matter (solid, liquid or gas) being
transferred, e.g. Mexican wave in a football crowd
Waves travel through
medium
sound waves
seismic waves
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No medium required
visible light
infrared rays
microwaves
other types of
electromagnetic
radiation
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Transverse or longitudinal waves?
Longitudinal waves
the vibrations are at right the vibrations are along the
parallel to the direction of
angles to the direction of
travel e.g.
travel e.g.
- sound,
- light,
- electromagnetic radiation, - P waves (a type of seismic
wave)
- water waves,
- S waves (a type of seismic
wave)
Transverse waves
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What are waves?
• The wavelength is the distance between a point on one
wave and the same point on the next wave
• The amplitude is the maximum distance of the particles
in a wave from their normal positions
• The frequency of a wave is the number of waves
produced by a source each second.
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How fast do waves travel?
• wave speed (m/s) = frequency (Hz) × wavelength (m)
wave
speed
frequency wavelength
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Reflection
• Sound waves and light waves reflect from surfaces.
The angle of incidence equals the angle of reflection
• Smooth surfaces produce strong echoes when sound
waves hit them
• Rough surfaces scatter sound and light in all directions
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Refraction
• Sound waves and light waves change speed when
they pass across the boundary between two
substances with different densities, e.g. air and glass.
• This causes them to change direction and this effect is
called refraction
• There is no change in direction if the waves cross the
boundary at an angle of 90° - in that case they carry
straight on (although there is still a change in speed).
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Electromagnetic spectrum
Wavelength () increases
Frequency (f) increases
Gamma
X-ray
UltraLight
Infra-red
Microwaves Radio
violet
Gate
X of a phrase
Usually
Letshelp you
Inremember
Radiation
Can
you
think
that would
Low Most
frequency
this order?
High
frequency
Highfrequency
frequency
Low
Long wavelength
Short wavelength
High energy
Short wavelength
wavelength
Long
Low energy
Most penetrating
Highenergy
energy
Low
Least penetrating
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Most penetrating
Least
penetrating
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Hazards of electromagnetic radiation
Microwaves
cause internal heating of body
tissues
Infrared radiation
is felt as heat and causes skin
burns
damage cells, causing mutations
(which may lead to cancer) and cell
death
X rays
Gamma rays
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also damage cells, causing
mutations (which may lead to
cancer) and cell death.
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The three main types of ultraviolet
radiation, and some of their effects
Type
UV C
UV B
UV A
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frequency hazard
causes severe damage to cells,
high
skin cancer
causes severe sunburn and
medium
damage to cells
low
weaker effects than UV B
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Uses of electromagnetic radiation
• Radiowaves – broadcasting,
communications & satellite
transmissions
• Microwaves – cooking, communications &
satellite transmissions
• Infrared - cooking, thermal imaging, short
range communications, optical fibres, TV
remote controls & security systems
• Visible light – vision, photography &
illumination
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Uses of electromagnetic radiation
• Ultraviolet – security marking,
fluorescent lamps, detecting forged bank
notes & disinfecting water
• X-rays - observing the internal structure
of objects, airport security scanners &
medical X-rays
• Gamma - sterilising food and medical
equipments, detection of cancer and its
treatment
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Exam tip
• To make your answer as full as possible you
should include:
1. the advantages and disadvantages of each type
of radiation
2. clearly indicate the precise use and why
3. include information about frequency and
wavelength
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Ionising radiation
• Alpha, beta and gamma are ionising radiation: they can
knock electrons out of atoms and form charged particles
• Radiation can be harmful, but it can also be useful - the
uses of radiation include to:
1. detect smoke
2. gauge the thickness of paper
3. treat cancer
4. sterilise medical equipment.
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Types of radiation
• Nuclear radiation comes from the nucleus of an atom
of substances which are radioactive
• All radiation transfers energy. There are three types of
nuclear radiation: alpha, beta and gamma
alpha
beta
gamma
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The solar system
• The solar system consists of:
1. a star - the Sun
2. satellites - moons - in orbit around most of the planets
3. comets and asteroids in orbit around the Sun.
4. eight planets, including the Earth, and smaller dwarf
planets, such as Pluto, Ceres and Eris.
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Space exploration
• The Search for Extra-Terrestrial Intelligence (SETI) is
a programme that uses radio telescopes to look for
non-natural signals coming from space
• Space probes photograph
planets looking for evidence of
life
• Space landers touch down on
planets and take a soil sample,
which is analysed for evidence
of life.
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What is a spectrometer?
• Spectrometer is an instrument that can split up
light to show the colours of the spectrum
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The origins of the Universe
• Scientists believe that the universe began in a hot
'big bang' about 13 billion years ago
• Two evidences of the Big Bang Theory are;
1. the existence of a microwave background
radiation,
2. red-shift.
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Other theories for the origin of the
universe
• The Oscillating Theory suggests that this universe is
one of many - some that have existed in the past, and
others that will exist in the future
• When the universe contracts in a Big Crunch, a new
universe is created in a new Big Bang.
• The Steady State Theory suggests that as the universe
expands new matter is created, so that the overall
appearance of the universe never changes.
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Life cycle of a star
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The future of other stars
• The life of stars depend on their masses . A heavyweight star will still become a red giant, but then:
1. it blows apart in a huge explosion called a supernova
2. the central part left behind forms a neutron star, or
even a black hole, if it is heavy enough
3. black holes have a large mass, and a large gravity - even
light cannot escape them because their gravitational
field is so strong
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A supernova is an
exploding star
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Evidence for the Big Bang Theory
• Red-shift - red is a longer wavelength of light, this
means that the galaxies must all be moving away from
us
• Cosmic Microwave Background radiation electromagnetic radiation which was present shortly
after the big bang is now observed as background
microwave radiation.
• A satellite called COBE mapped
the background microwave
radiation of the universe
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Evidence for the Big Bang Theory
Evidence
Interpretation
The other galaxies are moving away
The light from other
from us. This evidence can be used to
galaxies is redexplain both the Big Bang theory and
shifted.
Steady State universe.
The most likely explanation is that the
The further away
whole universe is expanding. This
the galaxy, the more
supports the theory that the start of
its light is redthe universe could have been from a
shifted.
single explosion.
The relatively uniform background
Cosmic Microwave radiation is the remains of energy
Background (CMB) created just after the Big Bang.
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Doppler effect for a moving sound
source
Long wavelength
Low frequency
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Short wavelength
High frequency
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Ultrasound and infrasound
• Sound waves are longitudinal waves that must pass
through a medium
• Ultrasound waves have a frequency above the normal
range of human hearing - they can be used to
1. scan for birth defects in unborn babies
2. scan for defects in manufactured equipment.
• Infrasound has a frequency below normal hearing can be used to
1. track animals
2. monitor seismic activity
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Sound waves
• When an object vibrates, it produces sound. The bigger the
vibrations, the greater the amplitude and the louder the
sound
• 1 and 2 - two sounds with the same frequency but
different amplitude. Sound 1 (smaller amplitude) is quieter
than sound 2.
• 2 and 3 - two sounds with the same amplitude but different
frequencies. The faster the vibrations, the higher the
frequency and the more highly pitched the sound.
• So sounds 2 and 3 have the same volume (loudness), but 3
(higher frequency) is higher pitched.
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Ultrasound
• When ultrasound waves reach a boundary between
two substances with different densities, they are partly
reflected back and detected
• e.g. sound travels through water at about 1,400 m/s. If
it takes 0.5 s for a sound to reach a boundary and
reflect back to the detector, the total distance travelled
is: distance = speed × time
= 1,400 × 0.50
= 700m
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Sonar
• Sonar is used on ships and
submarines to detect fish or
the sea bed.
• A pulse of ultrasound is sent
out from the ship.
• It bounces off the seabed or
shoal of fish and the echo is
detected.
• The time taken for the wave to
travel indicates the depth of
the seabed or shoal of fish
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Infrasound
• Infrasound has frequency less than 20Hz, this is below
the range that humans can hear (20-20,000Hz).
• Infrasound is detected using a microphone.
• Three uses of infrasound:
1. to detect volcanic eruptions - as a volcano erupts it
produces infrasound, which can be detected even if
the volcano is in a remote location far away
2. to track the passage of meteors through the
atmosphere
3. to track animals (elephats use infrasound to
communicate) even if they are hidden in dense
forests. This helps with the conservation and
protection of these animals.
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Seismic waves
• The crust and upper mantle are broken into large
pieces called tectonic plates.
• These plates move slowly, but can cause earthquakes
and volcanes where they meet.
• The seismic waves produced by an earthquake are
monitored and tracked.
- liquid nickel and iron
- Solid nickel and iron
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Seismic waves
• Earthquakes happen when large parts of the Earth's
crust and upper mantle move suddenly
• Earthquakes produce shockwaves called seismic
waves. These waves can be detected using
seismographs.
type of wave
relative speed
can travel
through
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P waves
longitudinal
faster
solids and
liquids
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S waves
transverse
slower
solids only
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Difference between S and P waves
• S-waves
- transverse
- slow moving
- travel through solids only
• P-waves
- longitudinal
- fast moving
- travel through liquids and solids only
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Producing electricity
• An electric current can be produced by moving a
magnet inside a coil of wire attached to a sensitive
ammeter, the needle is seen to move.
• This means the magnet causes the free electrons
to move around the circuit as a current
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Producing electricity
• Here the magnet is being pushed into
the coil.
• The ammeter shows current induced in a
positive direction.
• Now the magnet is stationary inside the coil.
• There is no current being produced in the
coil, shown by the zero reading on the
ammeter
• The magnet is being pulled out.
The ammeter shows current being
induced in the opposite direction to
before.
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Producing electricity
• The size of this induced current can be increased by
1. move the magnet faster
2. use a stronger magnet
3. increase the number of turns on the coil
4. increase the area of the coil.
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Direct and alternative current
• Direct current – DC, current flows in only
one direction .
• Batteries and solar cells supply DC
electricity.
• The diagram shows an oscilloscope screen
displaying the signal from a DC supply.
• Alternating current – AC, current constantly
changes direction.
• Mains electricity is an AC supply. The UK mains
supply is about 230V.
• It has a frequency of 50Hz, which means that it
changes direction and back again 50 times a
second.
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Producing electricity
• Generators (bicycle dynamo) induce a current by
spinning a magnet inside a coil of wire
• When this happens, a potential difference - voltage - is
produced between the ends of the coil, which causes a
current to flow.
• As the bicycle moves, the
wheel turns a magnet inside a
coil
•This induces enough electricity
to run the bicycle's lights
•The faster the bicycle moves,
the greater the induced current
and
the brighter the lights.
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Large-scale electricity production
• Turning generators indirectly - generators can be turned
indirectly using fossil or nuclear fuels
1. Heat is released from fuel and boils the water to make
steam.
2. The steam turns the turbine.
3. The turbine turns a generator and electricity is produced.
4. The electricity goes to the transformers to produce the
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correct
voltage
Different sources of energy
Renewable energy resources include:
• wind energy
• tidal waves
• hydroelectric power
• geothermal energy
• solar energy
• biomass energy, for example energy released from
wood
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Solar cells or Solar energy
• Solar cells (or photocells) turn light energy from the
Sun directly into direct current electricity.
Advantages
Disadvantages
Its renewable
No maintenance
No power lines required
No fuel
Long lifetime
No green house gases
Expensive to build
Low efficiency – requires
large area
Manufacture causes
pollution
Low power output
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Hydroelectricity
• A dam is built to trap water, usually in a valley where
there is an existing lake.
• Water is allowed to flow through tunnels in the dam, to
turn turbines and thus drive generators.
Advantages
Disadvantages
No waste or pollution
Very reliable
Low running cost
Quick start-up time
Electricity can be
generated constantly
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Requires hilly areas
Destroys habitats
Expensive to build
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Wind turbines
• Wind turbines (or aero-generators) use large blades to
capture the kinetic energy of the wind.
• This kinetic energy is used to directly turn a turbine
and produce electricity.
Advantages
Disadvantages
No waste or greenhouse
gases
No fuel is needed
Can be tourist attractions
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Noisy
May spoil views
Kill birds
The amount of electricity
generated depends on
the strength of the wind.
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Geothermal energy
• Hot rocks underground heat water to produce steam.
• Holes are drilled down to the hot region, steam comes
up to drive turbines, which drive electric generators
Advantages
Disadvantages
No pollution
No fuel is needed
Easy and cheap to run
Hot rocks are not
available everywhere
Geothermal site can run
out of steam
Hazardous gases or
minerals may come up
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Tidal power
• These work rather like a hydro-electric scheme, except
that the dam is much bigger.
Advantages
Disadvantages
Tidal range varies
High power output
Destroys habitats
Reliable power source
Expensive to build
Long lifetime
Low running costs
No fuel needed
Tides are predictable
Not expensive to maintain
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Biomass
• Wood is burnt to heat our homes and cook our food.
• Sugar cane can be fermented to make alcohol, which
can be burned to generate power.
Advantages
Disadvantages
The fuel is cheap
Less demand on the
fossil fuel
Difficult to collect or
grow large quantities
It produce greenhouse
gases
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Transformers
• Transformers are used in the National Grid to
reduce energy losses from the wires during
transmission.
• A transformer that increases the voltage is called a
step-up transformer
• A transformer that decreases the voltage is called a
step-down transformer e.g. adapters and rechargers
for mobile phones and CD players.
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Transformers
• The ratio between the voltages in the coils is the same
as the ratio of the number of turns in the coils
primary voltage
= turns on primary
secondary voltage
turns on secondary
• This can also be written as:
Vp/ = Np/
Vs
Ns
• Step-up transformers have more turns on the
secondary coil than primary coil.
• Step-down transformers have fewer turns on the
secondary coil than the primary coil.
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Transformers
• A transformer has 20 turns on the primary and 400 on
the secondary. What is the output voltage if the input
voltage is 500V?
Vp/
Np/ Therefore Vs/ = Ns/
=
Vs
Ns
Vp
Np
Vs/
400/
=
500
20
Vs = 500 x (400/20)
Vs= 10,000 Volts
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Current
• A current flows when an electric charge moves around
a circuit – measured as the rate of flow of charge
• The current flowing through a component in a circuit is
measured using an ammeter
• The units for current is amperes or A
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Potential difference (voltage)
• A potential difference, also called voltage, across an
electrical component is needed to make a current flow
through it.
• Potential difference across a component in a circuit is
measured using a voltmeter
• The voltmeter must be connected in parallel with the
component.
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Power, current and potential
difference
• Power is a measure of how quickly energy is
transferred.
• You can work out power using this equation:
power (W) = voltage (V) × current (A)
power
voltage
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current
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Power and energy
• Power is a measure of how quickly energy is
transferred.
• You can work out power using this equation:
energy
transformed
power
time
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Paying for electricity
• The amount of electrical energy transferred to an
appliance depends on its power, and on the length of
time it is switched on for
• The amount of mains electrical energy transferred is
measured in kilowatt-hours (kWh). One unit is 1kWh
energy transferred (kWh) = power (kW) × time (h)
• The cost of the electricity used is calculated using this
equation:
cost = power (kW) × time (hour) × cost of 1 kWh (pence)
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Saving energy (cost efficiency)
payback time = cost of energy-saving measure ÷ money
saved each year
• e.g. Double-glazing might cost £2,500 and save £100 a
year. What is the payback time?
= 2,500 ÷ 100
= 25 years
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Saving energy (cost efficiency)
• When buying an energy-saving device, it is important
to consider the advantages and disadvantages.
• Some disadvantages would be:
1. initial cost
2. use of extra resources to manufacture new device
3. cost of disposal of old device.
• Some of the advantages would be:
1. cost efficiency
2. saving energy and resources.
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Energy transfer and efficiency
• Forms of energy - Most Kids Hate Learning GCSE
Energy Names
• Magnetic - energy in magnets and
electromagnets
• Kinetic - the energy in moving objects.
Also called movement energy
• Heat – also called thermal
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Energy transfer and efficiency
• Light – also called radiant energy
• Gravitational potential – stored energy in
raised objects
• Chemical – stored energy in fuel, foods
and batteries
• Sound – energy released by vabrating
objects
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Energy transfer and efficiency
• Electrical – energy in moving or static
electric charges
• Elastic potential – stored energy in
stretched or squashed objects
• Nuclear – stored in the nuclei of atoms
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Energy transfers
• Different types of energy can be transferred from one
type to another, e.g. of useful energy transfer
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Sankey diagrams
• Sankey diagrams summarise all the energy transfers
taking place in a process.
• The thicker the line or arrow, the greater the amount of
energy involved.
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Calculating efficiency
• The efficiency of a device such as a lamp can be
calculated using this equation:
• efficiency = useful energy transferred x 100
energy supplied
• The efficiency of the filament lamp is (10 ÷ 100) × 100 =
10% - this means that 10% of the electrical energy
supplied is transferred as light energy (90% is
transferred as heat energy).
• The efficiency of the energy-saving lamp is (75 ÷ 100) ×
100 = 75% - this means that 75% of the electrical
energy supplied is transferred as light energy (25% is
transferred as heat energy).
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