P1.5 Flashcards
What is electric current and voltage?
current - rate of flow of charge around a circuit.flows from positive to negative
electrons carry the charge
voltage - electrical pressure, gives the measure of energ transferred
What is the difference between alternating and direct current?
a.c reverses direction back and forth, d.c always flows in the same direction
cathode ray oscilloscope shows current as a trace on a graph. a.c looks like a wave, d.c a straight line
a.c is used in things like mains electricity supply in a home, d.c is used in things like batteries and solar cells
What is electrical power?
How is it useful?
the energy transferred per second
electrical appliances convert it into other forms of energy
e.g light bulb converts it into light and heat energy
it tells you how quickly appliances transfer electrical energy
units of power, watts - higher the power the more energy transferred per second
e.g 100w light bulb is brighter than a 60w one
What experiment can calculate power?
make a circuit using an ammeter, a switch,a battery, and a test component in series
(ammeter will measure current flowing through the circuit)
connect a voltmeter to the circuit in parallel across the test component
close the switch to complete the circuit
there will be reading on the ammeter and voltmeter. record these numbers and use in the equation to calculate the power
power = current x voltage
How can you induce voltage/current?
electromagnetic induction - moving a magnet in/near a coil of wire
as the magnet moves, the magnetic field through the coil changes, the change induces voltage and current through the wire
the direction of the voltage depends on which way the magnet is moved
this can also be done by rotating a magnet in/near a coil of wire or rotating a coil of wire in a magnetic field
if you move a magnet into the coil, the voltage and current will be induced in the opposite direction from when the magnet is moved out of the coil
if you reverse the north/south polarity so the opposite poles point into the coil, the voltage and current will be induced in the opposite direction
What 4 factors affect the size of induced current and voltage?
strength of the magnet
number of turns on the coil
the area of the coil
the speed of the movement
to get a bigger voltage/current, increase one or more of these factors
for a smaller voltage/current, reduce one or more
if you move/turn the magnet faster, there will be a higher peak voltage and higher frequency as the magnetic field will be reversing more frequently
How do generators work?
they generate a.c by electromagnetic induction (rotating a magnet or coil of wire while magnet fixed)
they need something to do the turning e.g steam-driven turbine or water wheel
a dynamo is a generator used on bikes to power the lights. the magnet is rotated not the coil. it’s attached to the wheel so as the wheel turns so does the magnet
What are the problems with using non-renewables?
they release co2 which adds to the greenhouse effect and causes global warming
they release sulfur dioxide which causes acid rain. e.g burning coal
messes up the landscape e.g coal mining
environmental problems e.g oil spillages
nuclear waste produced, hard and dangerous to dispose of
high costs e.g nuclear power as the cost to build and decommission power plants is high
risk of disaster e.g nuclear power carries this risk
e.g Chernobyl disaster
How do power stations generate electricity?
fuel is burned in a boiler
this produces steam which turns the turbine
turbine turning powers the generator
chemical - heat- kinetic - electrical
What are nuclear reactors?
they use nuclear fission to produce heat and produce steam to drive turbines
What is hydroelectricity?
What are the positives and negatives?
usually involves flooding a valley by building big dams
rainwater is caught and allowed out through turbines,turning them as it leaves
negatives - big impact on environment
positives - immediate response to increased demand for electricity - more water let out through turbines and more electricity generated
reliable
initial costs high but running costs low
What is wave power?
What are the negatives of using it?
using waves to provide the up-down motion needed to turn the turbine and power the generator
unreliable - waves die down when wind drops
most electricity generated using waves close to shore although waves further out are more powerful (offshore wave farms being developed)
never likely to provide energy on a large scale
What are tidal barrages?
What are the pros and cons?
big dams built across river estuaries with turbines in
as tide comes in, water fills up estuary to height of several m and is allowed out through turbines at controlled bar.
turns the turbine as it leaves
positives - reliable
has potential to generate significant amounts of energy
negatives - can only be used in a few suitable estuaries
What is wind power?
What are the positives and negatives?
uses wind turbines each has a generator inside. electricity is generated directly from the wind turning the blades
positives - no pollution after manufactured
negatives - spoil the view
can be noisy
only work when windy
What are solar cells?
What are the positives and negatives?
they generate electric currents directly from sunlight
solar power often used in remote places
in sunny countries, it’s a reliable source but only during daylight hours
What is geothermal energy?
What are the cons?
water is pumped in pipes down to hot rocks then returns as steam to turn turbine and power generator
high setup cost
only available in very few places
What needs to be considered when setting up a power station?
set up costs - bigger ones more expensive as more engineering needed to make it safe
set up time - affected by size, complexity and planning issues
running/fuel costs - renewable usually lowest as no fuel involved
reliability issues - usually depend on weather so less reliable
environmental issues - if fuel involved, more waste and atmosphere pollution and uses up more finite fuel resources
all fuel - visual and noise pollution
also other problems e.g dangerous waste, explosions
renewable - disruption of wildlife habitats
location issues - solar, pretty much anywhere
gas - anywhere there’s pipes
hydroelectric - hilly,rainy places with floodable valleys
nuclear - has to be away from people
tidal - big river estuaries needed
geothermal - needs hot rocks near Earth’s surface
waves - has to be on coast
oil - near coast
How does electricity get around?
national grid takes energy to from power station to where it’s needed
enables power to be generated and supplied anywhere on the grid
needs either high voltage or current to transmit large amounts of power
high current - lots of energy lost as heat in cables due tp friction
better and cheaper to make voltage high and keep current low
What do pylons and transformers do?
for high voltage, transformers and pylons with insulators are needed
transformers step up a.c voltage at one end for efficient transmission and back down at the other end to safe usable levels
all have coils - primary and secondary, joined with iron core
step-up transformers increase voltage by using more turns on the secondary coil and step-down transformers decrease the voltage using more turns on the priumary coil
primary voltage/secondary voltage
=
turns on primary/turns on secondary
What are the problems with transmitting large amounts of energy?
not very efficient - high power losses
high voltage is a risk to people
some people worried about the long term health of people living near power lines
How can you save money on heating and electricity bills?
loft insulation hot water tank jacket cavity walls and insulation double glazing draught proofing
low energy and efficient appliances cheaper to run but more expensive to buy
How do you work out payback time?
payback time = initial cost / annual saving
How is energy measured?
in joules (j) or kilojoules (kj) 1kj = 1000j
amount of energy an appliance uses depends on power and time left on/used
electricity meters record the energy used in kilowatt-hours (kwh), which is the amount of energy used by a 1kw appliance left on for 1 hour
How do you work out power and cost?
power(w) = energy(j) / time
cost =power(kw) x time (h) x cost of 1kwh
