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p8 (gravity (orbits are almost circular, velocity is always changing,…
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gravity
orbits are almost circular
velocity is always changing, accelerating
centripetal force, directed towards the centre of the circle
force is provided by gravity, cause the object to fall towards what it orbits, but the object is already moving, so changes direction
object accelerates to what it orbits but velocity is always at right angles to acceleration, keeps it travelling in a circle
too fast, fly into space, too slow, spiral down crash into what it was orbiting
grav force is stronger the closer to the star/planet, closer you get, faster you need to go to stay in orbit
object moves faster, radius must be smaller, vice versa
earthing and fuses
electricity flows through anything that conducts, if live connects with metal, current will flow, can cause electric shocks and fires
appliances with metal cases must be earthed for safety, case must be attached to earth wire
a fault where live touches metal case, current will flow down the earth, earth is v thick, low resistance, total resistance of the circuit decreases
current = pd / resistance, causes big current to flow through live, the case, out down earth
surge in current melts fuse, breaks circuit, cuts off live supply, isolates appliance, impossible to be shocked, prevents fires
also protect circuits and wiring from getting fried is there is a current surge
non-conductive casing = double insulated, no need for earth, can't become live
national grid
network of wires and transformers that connects uk power stations to consumers
transfers energy electrically from power stations to where it's needed in homes and industry
need either high pd or current to transmit large amount of power needed
with high current, lose lots of energy as wires heat up and energy is transferred to thermal energy store of surroundings
power lost is p = i^2 x r
wasted energy and power cost money, cheaper to boost pd really high, keep current very low, makes national grid efficient in energy transfer
transformers
to get voltage to 400 000V for efficient transmission, use transformers
transformers have 2 coils, primary and secondary, joined with iron core
pd increased using step up transformer, more turns on secondary coil
decreased at local consumer up using step down
power supplied to a primary coil given by power = pd x current
nearly 100% efficient input power = output power, pd across primary x current in primary = pd across secondary x current in secondary
hydroelectricity
flooding a valley by building a big dam
rainwater caught and allowed out through turbines
bring impact on environment, possible loss of habitat
immediate response to increases demand, more water can be let through, turbines generate more electricity
initial costs are high, minimal running costs, reliable
wiring
neutral : blue, left, completes circuit, electricity flows in through live, out through neutral, always at 0V
live : brown, right, carries the voltage, alternates between voltage of about 230V
earth : green and yellow, middle, for safety, carries current away if something goes wrong, at 0V
pd between live and neutral equals supply pd, 230V for mains,
pd between live and earth is also 230V for mains connected appliances
no pd between neutral and earth, both at 0V, body also at 0V, if touches the live, could be a large pd across body, current would flow through, large electric shock, injury or death
solar system
made up of a star (the sun) and what orbits it
planets : large objects that orbit a star, from sun outwards, mercury, venus, earth, mars, jupiter, saturn, uranus, neptune
minor planets : planet like objects that orbit stars but don't meet rules for a planet eg pluto
natural satellites like moons, small things, orbit planets
artificial satellites : made made objects with specially designed orbits
tidal barrages
big dams build across river estuaries w turbines in them
tide fills estuary, water let through turbines at set speed
no pollution, affect boat access, spoil view, alter habitats
tides are reliable, height is variable, don't work when water level is same on each side
polar
sweep low and both poles, earth rotates beneath
closer to earth, once every 2 hours
scan the next bit of globe each orbit, monitors the whole earth each day
weather, mapping, surveillance
ac
ac produced by alternating voltage, pd and current constantly change direction
uk mains is ac at 50 hz and 230 v
dc produces by a direction voltage, found in batteries and cells
geostationary
high orbit over equator, once every 24 hours
stay above the same point on earth's surface, earth rotates with them
communications, stay at same point, easy to point transmitters and receivers at them, transfer signals from one side of earth to other in fraction of a second