Electricity - Mains electricity and safety Flashcards
period
time taken for one complete oscillation (s)
frequency
number of full cycles per second (Hz)
frequency =
1 / period
what is the UK mains voltage
230V
what is the UK mains frequency
50Hz
difference between AC and DC
AC gives current that is constantly alternating between positive and negative
AC comes from the mains power supply
DC gives current in one constant direction
DC comes from batteries and fuel cells
dangers of high current and ways to prevent
higher temperature
allowing too much current through can lead to high fire/burn risks
thicker wires are needed for higher currents
fuse/circuit breaker
what is a fuse
intentional weak point in a circuit
- higher fuse values cause for thicker wires
-You should always fit a fuse that is
rated closest to your appliances’ current, but is higher.
what fuse should an appliance be fitted with
a fuse most similar to the voltage of the appliance, but above. eg; 4V appliance with a 5V fuse
earthed appliances
large current flows from live wire to earth wire
this causes the fuse to blow
the appliance is safe because the circuit has been broken due to the EARTH WIRE and THE FUSE
what does an earth wire do
provides a low resistance pathway to earth
what is a lightning rod
a very large earth wire that protects buildings instead of appliances
- usually made of copper as they are very good conductors of electricity
how will a material become positive
by losing electrons due to friction
how will a material become negative
by gaining electrons due to friction
why are plastics more likely to become electrically charged than metals
metals are conductors and their electrons are free to move around within the material
plastics are insulators
advantages of connecting heaters in parallel
- improved efficiency
- more energy can be delivered than would be in series
- power shared equally between the heaters
- others will continue to work even if one fails
advantages of connecting heaters in series
single switch to control all
current/voltage graph of a wire at constant temperature
directly proportional
current/voltage graph of a diode
flat then sharp increase
current/voltage graph of a filament lamp
the current does not increase as fast as the potential difference
effect of light intensity (of an LDR) on resistance
higher light intensity leads to lower resistance
