Physics Unit 2

Physics Unit 2

1. Using the Sun's energy

   • The Sun is the ultimate source of loads of our energy
     • The Sun has been giving out loads of energy-mostly heat and light
     • Some of that energy is stored here on Earth as fossil fules
     • We can also use photocells and solar heating
   • You can capture the suns energy using photocells
     • Photocells generate electricity directly from sunlight
     • They generate diret current (DC)
       • Direct current means the current flows the same round the circuit all the time
     • Photocells are usually made of silicon
       • The silicon atombs absorb some of the energy, knocking loose some electrons
       • These electrons then flow round a circuit-which is electricity
     • The current and power output of a photocell depends on
       • It's surface area
         • The bigger the cell the more electricity it produces
       • The intensity of light
         • brighter light=more electricity
       • The distance from the light source
         • The closer the cell, the more intense the light hitting it will be
     • Advantages
       • There are no moving parts
       • Sturdy, low maintenance and lasts a long time
       • You don't need power cables or fuel
       • Solar power won't run out and it does not pollute the enviroment
     • Disadvantages
       • No sunlight, no power
   • Curved mirrors can concentrate energy from the sun

2. Solar and Wind power

   • Passive solar heating
     • PSH is when energy from the sun is used to heat something directly
     • Glass lets heat and light in from the sun
   • Wind Farms
     • Lots of little wind turbines
     • Uses wind to produce electricity

3. Producing and Distributing Electricity

   • The national grid connects power stations to consumers
     • The national grid allows electricity to be supplied anywhere around the country
   • There are different power sources
     • Fossil Fules
       • Produces a lot of energy
       • Releases a lot of carbon-dioxide
     • Biomass
       • It is a renewable source
       • You need a lot of it
     • Nuclear Power
       • Does not produce a lot of CO2
       • Can make a lot of energy without producing a lot of CO2
       • Risk of leaks and disasters
     • Photo cells
       • Advantages and disadvantages in Red
     • Wind Power
       • Cheap to run
       • 1500 turbines=one coal powered stations

4. The Dynamo Effect

   • Electromagnetic Induction
     • The creation of a voltage in a wire which is experiencing a change in magnetic field
   • Move the wire or the magnet
     • Two ways to get EMI
       • An electrical conductor (a coil of wire is used often) moves through a magnetic field
       • The magnetic field through an electrical conductor changes (gets bigger, smaller or reverses
     • To get a bigger voltage
       • The strength of the magnet
       • The umber of turns on the coil
       • The speed of movement
   • Generators move a coil in a magnetic field
     • Every half turn, the current in the coil swaps direction
       • This means that generators produces an alternating current (AC)
         • Turning the coil faster produces
           • More pearks
           • A higher voltage
           • A higher current
           • The frequency of AC is measured in Hz
             • Electricity in the UK is 50 Hz
               • Meaning that the coil is rotating 50 times per second

5. Supplying electricity efficiently

   • Electricity is transformed to high voltage before distribution
     • To transmit a lot of power you need
       • A high voltage
       • A high current
         • But a high current means the cables get hot
       • It is cheaper to increase the voltage
         • To bring down voltage you need a step-down transformer (AC)
           • This is why mains energy is AC so that transformers work
         • To increase voltage you need a step-up transformer (AC)
   • Power stations aren't very efficient
     • Power stations make a lot of waste energy
       • Total Energy=Useful energy output + waste energy output
         • Efficiency=Useful energy output/total energy input (x 100)

6. Electrical Power

   • Running costs depend on an appliances power rating
     • Power (W) = Voltage (V) x Current (A)
   • Kilowatt-hours (kWh) are units of energy
     • Energy Supplied (kwh) = Power (kW) x Time (H)
       • Cost = number of units x price per unit
     • kWh = amount of energy converted by 1 kW appliance left on for 1 hour
   • Off-peak electricity is cheaper

7. The green house effect

8. Global warming and climate change

   • Upsetting the greenhouse effect has led to climate change
     • Evidence shows that the rising of CO2 is causing global warming.
       • There is a scientific consensus the humans are causing global warming
   • Changes to the weather can have human and natural causes
     • Changes in temperature can have large effects on weather
       • Some crops won't be able to grow

9. Nuclear radiation

   • Nuclear radiation causes ionisation
     • Ionisation is when alpha, beta or gamma radiation hits atoms causing them to lose (positive) or gain (negative) electrons
       • Alpha particles are big and heavy
         • Strongly ionising
         • Easily stopped
       • Beta particles are electrons
         • Moderately ionising
         • Mediumly stopped
       • Gamma rays are very high frequency electromagnetic waves
         • Weakly ionising
         • Hard to be stopped
       • When radiation enters human skin it damages cells, can cause mutations

10. Uses of nuclear radiation

    • Alpha radiation is used in smoke detectors
    • Beta radiation is used in tracers and thickness gauges
    • Gamma radiation has medical and industrial uses
      • Can treat cancers
      • Sterilise medical instruments
      • Non-destructive testing

11. Nuclear power

    • Nuclear power uses Uranium as fuel
      • Uranium atoms split in 2
        • Water used as coolant to produce steam
          • Steam powers turbine which produces kinetic energy
            • This then goes into a generator which creates electrical energy
    • Advantages
      • Doesn't release alot of CO2
      • Realises a lot of energy
      • It is cheap
      • Plenty of uranium left
    • Disadvantages
      • Expensive to build and maintain
        • Expensive to decomision
      • Longer to start up
      • Risk of leaks
      • Uranium non-renewable source

12. Danger from radioactive matirials

    • You should always protect yourself
      • Handle with tongs
      • Store safely
      • Keep at arms length
      • Don't look at it
      • Industrial workers have
        • Full protective suits
        • Lead-lined suits
        • Lead/concrete barriers
        • Thick lead screens
        • Remote-control robot arms
    • Radioactive waste is hard to dispose of
      • High level
        • Stored underground in glass cases
      • Low level
        • Put in land-fill sites

13. The Solar System

    • Planets reflect sunlight and orbits the sun in ellipses
      • Our star (the Sun) has lots of stuff orbiting it
        • Mercury
        • Venus
        • Earth
        • Mars
        • Asteroids
        • Jupiter
        • Saturn
        • Uranus
        • Neptune
    • The solar system is held together by gravitational attraction
      • Gravity pulls everything in the universe towards everything else
        • Gravity makes things that are already moving change course

14. Asteroids and Comets

    • There's a belt of asteroids orbiting between Jupiter and Mars
      • When the solar system was formed the large rocks between Jupiter and Mars didn't form a planet as the large gravitational pull from Jupiter kept interfering
        • This left millions of asteroids orbiting the sun between Mars and Jupiter
      • Asteroids usually stay in their orbit but sometimes they are pushed or pulled into others
    • Meteorites are rocks that have crashed down to Earth
      • As the enter Earth's atmosphere they burn up
        • These are known as shooting stars
        • Sometimes, rarely, they don't burn up and they crash into the Earth's surface
          • They can start fires, throw lots of hot rocks and dust into the air
          • They make big holes in the ground called craters
          • The dust and smoke can block out the sun for many months
            • This causes climate change and can make animals extinct
    • Comets orbit the sun in very elliptical orbits
      • Comets are balls of rock, dust and ice which orbit the Sun
        • They come form objects orbiting around the sun way beyond the planets
          • As comet approaches Sun, it's ice melts leaving a bright tail of gas and debris which can be millions of KM long
            • This is what is seen from Earth
            • Comets speed up when the get closer to the Sun as of it's gravitational pull

15. NEOs and the Moon

    • Near-Earth objects could colloid with Earth
      • NEOs are meteors or comets that are o course to crash into Earth
        • Scientist calculate the trajectory of the NEO using powerful telescopes
          • Small NEO are harmless but the big ones can make an explosion bigger than a nuclear bomb
            • We could tr to deflect the NEO using a bomb to nudge it off course
    • The moon may have come from a colliding planet
      • Scientist think the moon came from another planet colliding with the Earth soon after the planet was formed
        • In the collision it is believed the Earth core was created when the planets collided
          • The less dense material was ejected as really hot dust and rocks which orbited the Earth eventually came together to form the Moon
            • Evidence to support this
              • The Moon has a lower density than the Earth
              • It does not have an iron core
              • Moon rock contains few substances which evaporate at low temperatures
                • Suggesting that the moon was made from hot matirials

16. Beyond the Solar System

    • We're in the Milky Way Galaxy
      • Our Sun only one of millions of stars in the Milky Way
      • Gravity keeps Galaxies together
    • The Universe has more than a billion Galaxies
    • Distances in space are measured in Light Years
      • Km are hard to measure between Galaxies
        • Scientists use light years
          • Light Years=The distance light travels through a vacuum in a year
    • Stars can explode and sometimes leave behind black holes
      • When a big star runs out of fuel it explodes and what is left it really dense
        • Sometimes it is so dense nothing can escape it's gravitational pull.
          • This is called a black hole
        • Black holes have a
          • Large mass
          • Small volume
          • Very high density
        • They are not visible not even light can escape it

17. The origin of the Universe

    • The universe seems to expanding because of redshift
      • Red shift is when scientists look at what colour galaxies are and this determines how far away it is using the visible light spectrum
        • The further away the galaxy is the more red it is
        • There are microwave radiation everywhere-it is known as cosmic background radiation
          • As the universe and cools, the background cools and drops in frequency
          • The universe started with the big bang
            • This is when all that was in the universe was all gathered in one small space
              • It then exploded and started expanding and the expansion continues
                • The big bang allows us to see how old the Universe is
                  • It is about 14 billion years old
                  • It is hard to estimate as it is hard to tell the change in the speed of expansion since the start

18. The life cycle of stars

19. Exploring the solar system

    • We can explore space using manned spacecraft
      • The solar system is big
        • Sending a manned spacecraft to Mars would take years
          • It would have to carry
            • A lot of fuel
              • This makes it heavy and expensive
            • Lots of food, water and oxygen
              • To keep the astronauts alive and healty
            • A sheild
              • To protect the astronauts from radiation
          • The astronauts will lose bone tissue and muscle wasteage from the low gravity
          • A tiny area with the same people could become stressful
    • Sending unmanned probes is much easier
      • Advantages
        • They don't have to carry food, water and oxygen
        • Can withstand conditions that humans can't
        • Without people, more instruments can be fitted
        • They're cheaper
        • No one gets hurt if the probe burns up in the atmosphere
      • Disadvantages
        • They can't think for themselves
        • A spacecraft can't do maintenance and repairs-people can

20. Galileo and Copernicus

    • Ancient Greeks thought the Earth was at the centure of the Universe
      • Most Ancient Greeks believed the Sun, man and other planets and stars all orbited Earth in perfect circles
        • The Ptolemaic model was the model of the Universe of the Ancient Greeks until the 1500s
    • Copernican Model
      • This model states that Earth and the planets orbit around the sun, which is at the centre of our Universe
        • The idea had been around for 2000 years but it was first published in 1543 in a book by Copernicus
          • Galileo noticed that Venus has phases-where the amount off the planet that was lit by the Sun seemed to change over time
            • Copernicans' ideas weren't very popular as the others had been their for a long time
              • The model was also condemned b the church. They claimed that the model went against the bible, and said that Earth was at the centre of the universe
                • Evidence for Copernican model increased thanks to more technological advances
                  • The current model says that the planets still orbit the sun but these orbit are elliptical rather than circular
      • Galileo fond one of the best pieces of evidence for this theory
        • Galileo was observing Jupiter using a telescope when he saw some stars in a line near the planet
          • He looked again and sore that these stars never moved away from Jupiter and seemed to be carried along with the planet
            • This suggested they weren't stars but moons orbiting Jupiter
              • This showed not everything orbits around the Earth

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