P5 - electricity in the home Flashcards
what is direct current (DC)
current that only goes in one direction
what is alternating current (AC)
a current that repeatedly reverses it’s direction
what is an alternating currents frequency
the number of cycles it passes through each second
what is the mains frequency in the UK
50Hz
compare the potential difference in an AC and DC circuit
AC - PD repeatedly reverses it’s direction
DC - PD does not change direction
where is the neutral wire earthed
the local electricity substation
why is the live wire dangerous
it’s potential repeatedly changes from + to - in every cycle
what voltage does the live wire reach in uk homes
325 V
what are step up transformers used for
to transfer electricity to the national grid
what do step up transformers do
increase size of the alternating current from around 25000 V to 132000 V
what are step down transformers used for
to supply electricity from the national grid to consumers
how much power are factories provided witth
100kV or 33kV
how much power are home supplied with
230V
how is the national grid efficient
the pd is very large, less current is needed to transfer same amount of power
power loss due to resistance heating in cables is reduced
what is the equation to measure frequency of an AC supply
frequency = 1/time taken for 1 cycle
what does the earth wire do
stops the metal case in a plug becoming live if the live wire breaks
why are the pins in a three pin plug made of brass
brass is a good conductor
doesn’t rust or oxidise
why is the case of a plug shaped a certain way
so the wires and pins can’t touch eachother
where is the brown wire connected to in a plug
the live pin
where is the blue wire connected to in a plug
the neutral pin
where is the green and yellow striped wire connected to in a plug
the earth pin
why is copper used for the wires in a plug
good electrical conductor
bends easily (ductile)
why is plastic used for the cable in a plug
good electrical insulator
if anyone touches the cable they don’t get shocked
what is the equation connecting power, energy, and time
p = e/t
what is current in an electrical appliance
the charge that flows through it each second
what is pd in an electrical appliance
the energy transferred to the appliance by each coulomb of charge that passes through it
what is the equation linking power current and pd
p = i x v
PEE ON IVY
what are the three fuse options domestic appliances are fitted with
3A
5A
13A
what is the equation linking power, current, and resistance
power = current^2 x resistance
what equation do you use to check the correct rating for a fuse
electrical power (watts) / potential difference (volts)
what is the equation for charge flow
charge flow = current x time
how does a resistor become hotter
electrons pass through resistor and collide with vibrating metal ions of resistor transferring energy to ions
ions gain kinetic energy, vibrate more
resistor becomes hotter
how do you calculate energy in a resistor (2 options)
energy = charge flow x pd
energy = power x time = pd x current x time
when charge flows around a circuit, what is the energy supplied equal to
the energy transferred to all the components in a circuit
what is the equation linking power, current, and potential difference
power = current x pd
what is the equation for efficiency
output power/input power x 100
can the efficiency of an electrical appliance be 100% ?
no it’s always less than 100%
why/how do electrical appliances waste energy
current in wires and components has a heating effect due to resistance of wires and components
energy is transferred by heating to surroundings
