Year 10 Physics Revision

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Year 10 Physics Revision
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Physics 1

• Waves
• The Universe
• Energy

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Waves

• Copy the above diagram and write down the units
  of amplitude and wavelength

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Waves

• Frequency is the number of waves which pass a
  point in 1 second.
• Frequency is measured in Hz
• So what does it mean if a wave has frequency of
  50Hz

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Waves

• Wave speed Wavelength x frequency
• Wavelength wave speed frequency
• Frequency wave speed wavelength

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Electromagnetic Spectrum

• This is a group of waves including light
• All e.m. waves
• Travel at the same speed
• Transfer energy from place to place
• Raise the temperature of the material that
  absorbs them
• Can be reflected and refracted

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Electromagnetic Spectrum
You are woken up in the morning by a radio alarm
clock. You go downstairs microwave some porridge
and use an infrared remote to turn on your TV.
Your TV sends out visible light. Then you go
outside and ultra-violet waves from the sun hit
you. Distracted you trip over and break a leg,
at the hospital you have an x-ray. On the way
out you walk past the cancer department where
they use gamma rays to save people.
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Refraction
Light bends towards the normal when it enters a
more dense medium. It bends away from the normal
when it exits. Draw a diagram of light exiting
glass
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Total Internal Reflection

• Happens when exiting more dense medium
• When angle is greater than the critical angle no
  light can escape

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Advantages of Optical Fibres

• The glass is lightweight compared to copper so
  they are cheaper to install
• Optical fibres are more difficult to bug than
  copper wires
• More information can be transmitted on a single
  optical fibre
• Less energy is used to send signals

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The Solar System
Planet Made of
Mercury Rock
Venus Rock
Earth Rock
Mars Rock
Jupiter Gas
Saturn Gas
Uranus Gas
Neptune Gas
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The Solar System

• Asteroids are lumps of rock left over at the
  birth of the solar system
• Comets are lumps of ice and dust which have
  highly elliptical orbits. They speed up as they
  approach the sun and slow down as they move away.
  Their tails always point away from the sun
  because of radiation pressure.

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Formation of the Solar System
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Nuclear Fusion

• Scientists used to think that the sun burns
  hydrogen, but if that was true the sun could only
  be around 800 years old since hydrogen burns
  quickly. Geologists have calculated that the
  Earth is millions of years old so the sun must
  release energy some other way.
• In stars elements combine in nuclear fusion to
  produce heavier elements and energy

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Nuclear Fusion
Hydrogen
Hydrogen
Lots of energy as heat and light
Helium
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Stars are in a constant balancing act between
gravitational forces inwards and pressure outwards
In main sequence stars these are balanced. This
can last for around 10 billion years.
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Life Cycle of a Small Star
Main sequence star, it is stable and doesnt
change size (sometimes called yellow dwarf)
Red giant, when the hydrogen runs out in a yellow
dwarf star the core shrinks and starts new fusion
reactions creating heavier elements. This
increases the radiation pressure which makes the
star larger
The red giant eventually looses its outer layers
and a core (called a white dwarf) is left. This
core eventually cools down into a black dwarf
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Life Cycle of a Large Star
Stars between 5 to 25 times the size of our sun
expand into red supergiants when they run out of
fuel. Eventually when the red supergiants run
out of fuel they collapse very quickly and cause
a massive explosion called a supernova. During
the explosion heavy elements such as gold are
created. Depending on the size of the star the
supernova will either leave behind a neutron star
or black hole
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Red Shift

• When we look at a spectrum of light from a
  burning gas it has several black lines on it.
  These lines are fingerprints telling us what
  elements are in the gas.
• When looking at light from galaxies we find that
  these lines are shifted towards the red end of
  the spectrum. The further a galaxy is away from
  us the more shifted the lines are.
• This tells us the galaxies are moving away from
  us, and the further they are away from us the
  faster they are travelling. This means the
  universe must be expanding

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Big Bang Theory

• If the universe is expanding then a long time ago
  it must have been very close together.
• The big bang theory states that the universe
  began with a big explosion. We can still see the
  energy from this explosion which we call
  background radiation

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Power Plants
See powerpoint powerstations on the physics
page
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National Grid

• Network of power lines which connects power
  stations together to supply us with electricity
• It is designed so that if one power station stops
  working another can take its place

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Transformers

• Transformers change voltage and current of
  electricity
• A step up transformer is used between powerplants
  and the national grid to increase the voltage,
  which decreases current, which decreases energy
  loss.
• A step down transformer is used between the grid
  and our homes to decrease the voltage to make it
  safe

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Power

• Power is measured in Watts (W) and tells us how
  many Joules are transferred every second
• 1W means 1 Joule is transferred every second.
• Power Voltage x Current
• 1 kW 1000W

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Cost of Electricity

• Number of units used (kWh) power (kW) x time
  (h)
• Cost number of units x cost per unit

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Energy Efficiency

• Efficiency is the percentage of energy supplied
  which is transferred into useful energy by a
  device
• Efficiency (useful energy transfer total
  energy input) x 100

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Payback Time

• Payback time is how long it takes you to recover
  the costs of an energy saving device.
• Example if a solar panel costs 4000 and saves
  you 500 a year the payback time would be 4000
  500 8 years

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Heat Transfer - Conduction

• Conduction is when heat is transferred through
  solids
• Conductors conduct heat fast (e.g. metals)
• Insulators conduct heat slowly (e.g. air, glass)

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Heat transfer - Convection

• Convection is heat transfer in a gas or liquid
• Convection happens because hot gases/liquids rise
• You can stop convection by trapping air (e.g. in
  fibre glass)

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Heat Transfer - Radiation

• Heat transfer by radiation is by electromagnetic
  waves (infra-red)
• Radiation can pass through matt black surfaces
  easily
• Radiation is reflected by shiny metallic surfaces
• All objects emit radiation

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Insulating our homes

• Each insulation method stops one or more of the
  heat transfer methods
• By using insulation we reduce the heat loss from
  our house so we use less fuel heating it.

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Insulation Methods

• Cavity wall insulation
• Lost insulation
• Double glazing