physics 2

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  • physics 2
    • electricity from the sun
      • passive solar heating
        • the floor absorbs the sun energy and emits energy at a different wave length, warming up the room.
      • photo cells
        • take energy from the sun to produce electricity, they produce a direct current. they have an anti-reflective layer
          • photo cells transfer light into electricity, producing a direct current. they can operate in remote locations. the energy is absorbed by photo cells. it works by knocking electrons lose from the silicon atoms in the crystals, meaning electrons can move freely.
          • the current and power of a photo cell depends on
            • light intensity- greater light intensity, greater the current produced
            • surface area - the more surface area exposed the higher the current produced
            • distance from light - closer the light source, the higher the current produced.
        • advantages
          • no moving parts, so lasts a long time.
          • no need for power cables
          • no need for fossil fuel - renewable
        • disadvantages
          • doesn't work at night or bad weather
          • need a large area of photocells to generate the necessary amount
      • solar stove
        • the sun hits a curved mirror and flashes on to a certain point.
    • other ways to use sun energy
      • passive solar heating
        • glass is transparent to the suns radiation, the sun radiation goes through the glass due to its short wavelength. its energy heats the surfaces and causes them to emits infrared radiation, at a longer wavelength. the glass reflects this wave. keeping the room heated.
      • wind turbines
        • advantages
          • renewable
          • produces less pollution
        • disadvantages
          • visual pollution
          • dependency on wind speed
          • kills birds
          • high maintenance
      • curved mirror
        • focuses light into one place, as a great deal of energy is focussed there, this place can get very hot. light energy from a large area is reflected by a curved mirror onto a cooking pot.
      • tracking the sun
        • the mirrors on solar collectors have monitors, so that they can track the position of the sun during the day and keep reflecting the light energy onto the same place.
    • generating and distributing electricity
      • producing electricity
        • the fuel is burned to boil water to make steam. steam then makes a turbine spin. the spinning of a turbine turns a generator which produces electricity. the electricity then goes to the transformers to produce the correct current. its then stored by the national grid until required.
    • the dynamo effect
      • how do simple AC generators work?
        • there is relative motion between a coil of wire and a magnetic (magnetic field)
          • move a piece of wire between the poles of a magnet. this creates a voltage. an electric current then pass through the wire, giving a reading on a sensitive amp-meter.
            • this is called the dynamo effect. as the wire passes through the magnet field between the poles of the magnet or by moving a magnet closer to a piece of wire.
              • the wire or magnet must be moving for a voltage to be induced, and there is no current if the wire is still.
        • to increase the current: use a large strength magnet, speed up the magnets movement or have more coils of wire.
      • step up transformers
        • we increase the voltage of electricity, to decrease the current so less energy is give to the surroundings.
      • power= current x voltage
      • step down transform
        • turns the voltage down so its safe to be around humans
    • power and paying for electricity
      • the amount of energy used by an electrical appliance id measured in kilowatt hours or units. the amount of energy spends on the power of the appliance and the length of time it is switched on for
      • cost = number of units x cost per unit
    • nuclear power
      • alpha
        • stopped by skin/ paper
      • beta
        • stopped by a sheet of aluminium
      • gamma
        • stopped by thick lead or concrete
      • all three of the nuclear radiation are called ionising radiation. this means the radiation causes electrons to be added or removed from atoms forming charged ions
        • alpha particles are the most ionising and gamma rays the least. when DNA in your cells is ionised it can severally damage the DNA causing cancer.
      • nuclear radiation can be detected by using  geiger-muller tube connected to a counter
      • advantages
        • large amounts of electricity can be generated
        • the fuel is available, and will not run out
        • no pollution is produced
      • disadvantages
        • cost of building & decommissioning are high and so fuel will have to cost lots
        • fuel has to be processes before it can be used
        • nuclear plants are slow to set up
        • expensive to process radio active waste & stored waste may be future terrorist target
        • always a risk of an accident that could damage the environment
    • uses of nuclear raiadtion
      • ionisation is when an atom collides with a neutron knocking off electrons, making it unstable and dangerous
        • ionising radiation can be used to kill cancerous cells- we use gamma rays (gamma knife)
      • beta is used to control paper thickness
        • paper passes between a beta source and a detector, which counts the. when less beta can get through, the rollers are loosened to increase thickness, if too much beta gets through the rollers get heavier.
      • alpha ionises the air, smoke detector contain metal plates and radioactive substance (alpha), which noises the air, which allows a current to flow, because electrons have been knocked off. smoke absorbs the alpha particles, so they no longer ionise the air, triggering the alarm.
        • smoke blocks the current.
    • the solar system
      • asteroids
        • are small pieces of rock which orbit the sun. most are from the formation of the universe. asteroids are most common between mars and jupiter, inside the asteroid belt
      • comets
        • is a large ball of ice and dust. they orbit the sun in an elliptical shape. it travels really far from the sun or really close. the closer they are to the sun the quicker they travel due to the suns gravitational pull. the sun's solar winds melt part of the comet leaving its trail of debris
      • asteroids of comets that could hit earth are called near each objects (NEO's). observations of NEOs may be used to track their trajectories, that way we can tell if they might hit earth.
      • the moo is the planets only natural satellite. its believed that the moon was formed by a planet colliding with a young east. the two elements such as iron, sunk to the centre, which less dense elements were thrown into orbit, forming the moon.
    • the big bang
      • the big bang theory states that a small state of matter expand to produce new elements and forces. hydrogen and helium were made first.
        • the state of matter expanded and as it did so cooled.
          • atoms, mainly hydrogen and helium began to form at 3000 degrees c
            • gravity causes the atoms to dump into galaxies and stars
              • Edwin hobble observed that the universe was expanding in every direction at a proportional rate. if a galaxy is twice as far away, it is moving twice as fast.
      • the doppler effect
        • when a car is moving towards you, the sound waves in front of the car are squashed together. when the car is moving away from you, the sound waves behind the car are stretched out. this increases the wave length and lowers the pitch.
        • the doppler effect means that sound moving away from an observer appears to be a lower frequency.
        • the same thing happens with light, from distant galaxies, which appeared to be shifted towards the low frequency, red end of the spectrum. this means distant galaxies must be moving away from the earth. it has also been observed that the further away a galaxy is, the greater the red shift. this means distant galaxies must be moving faster than near, all of which is evidence of the big bang theory
      • evidence
        • data on redshift. redshift shows us that galaxies, which are furthest away from are moving the faster than close galaxies
        • like the sparks of a firework, the sparks moving the fastest travel the furthest.
        • if you could run back time, all the sparks start at one point. its the same for galaxies
    • life cycle of stars
      • star birth and life
        • a huge ball of gas (nebula) begins to be pulled by gravity. a large ball of gas forms in the centre of this cloud. as it gets denser, more gas is pulled in. the ball gets hotter forming a proto-star. this continues to grow until it gets so big and the centre gets so hot, that the atoms get squashed together in a process called nuclear fusion. a star is born.
      • dying stars
        • small stars gradually cool and expand to become a red giant. the outer layer breaks away and forms a planetary nebula. all that remains is the white core. this white dwarf gradually cools over time. Larger  stars also eventually expand and cool, but grow much bigger. they turn into super red giants. the star then explodes, called a super nova. a star often outshines the others when a supernova happens.
        • during a super nova, the stars core is crushed own by intense gravitational forces. this can form a very dense star made up of only neutrons. this neutron star spins ver fast and sends pulses of radio waves to the earth. if the star is even bigger, the core is crushed into a tiny space to form a black hole. Black holes have gravity so strong that nothing can escape them.
      • black holes and density
        • black holes have near infinite densities due to their tiny volumes. all the mass of the core is crushed down into a space smaller than an atom. if you get too close yo a black hole, you will get sucked in.
    • Galileo & copernicus
      • copernicus realised that the sun had to be at the centre of the universe
      • Galileo decided to work on this idea. he developed a powerful telescope which showed him the moons of jupiter, proving the earth was to the centre.
      • these new ideas were very controversial,and went against the church. it was a crime to go against the church, so many scientists were scared to come out.

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