P1.5

Question 1

What is electric current and voltage?

Answer 1

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

Question 2

What is the difference between alternating and direct current?

Answer 2

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

Question 3

What is electrical power?

How is it useful?

Answer 3

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

Question 4

What experiment can calculate power?

Answer 4

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

Question 5

How can you induce voltage/current?

Answer 5

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

Question 6

What 4 factors affect the size of induced current and voltage?

Answer 6

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

Question 7

How do generators work?

Answer 7

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

Question 8

What are the problems with using non-renewables?

Answer 8

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

Question 9

How do power stations generate electricity?

Answer 9

fuel is burned in a boiler
this produces steam which turns the turbine
turbine turning powers the generator

chemical - heat- kinetic - electrical

Question 10

What are nuclear reactors?

Answer 10

they use nuclear fission to produce heat and produce steam to drive turbines

Question 11

What is hydroelectricity?

What are the positives and negatives?

Answer 11

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

Question 12

What is wave power?

What are the negatives of using it?

Answer 12

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

Question 13

What are tidal barrages?

What are the pros and cons?

Answer 13

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

Question 14

What is wind power?

What are the positives and negatives?

Answer 14

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

Question 15

What are solar cells?

What are the positives and negatives?

Answer 15

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

Question 16

What is geothermal energy?

What are the cons?

Answer 16

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

Question 17

What needs to be considered when setting up a power station?

Answer 17

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

Question 18

How does electricity get around?

Answer 18

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

Question 19

What do pylons and transformers do?

Answer 19

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

Question 20

What are the problems with transmitting large amounts of energy?

Answer 20

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

Question 21

How can you save money on heating and electricity bills?

Answer 21

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

Question 22

How do you work out payback time?

Answer 22

payback time = initial cost / annual saving

Question 23

How is energy measured?

Answer 23

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

Question 24

How do you work out power and cost?

Answer 24

power(w) = energy(j) / time

cost =power(kw) x time (h) x cost of 1kwh