Elecrtical Power And Mains Supply Flashcards
(27 cards)
what is the equation linking time in seconds, current, voltage and energy in j
e = IVt
What is work done equal to
Energy transferred
name some safety features built into domestic appliances
- double insulation
- earthing
- fuses
- circuit breakers
what kind of material do we wrap wires in
rubber
what is it called when an appliance does not have a metal casing
double insulation
why is earthing beneficial
-provides low resistance path to earth
- causes a surge of current in the earth wire and hence the live wire
- high current causes fuse to melt and break
- which cuts off supply of electricity to appliance
advantage of having a circuit breaker over a fuse
doesnt melt or break, so can be reset and used again
works much faster
what is current
the rate of flow of charge
why does temperature of resistor increase
due to collisions of free electrons within the wire
how is heat dissipated into surroundings used in domestic contexts
- electric heaters
- electric ovens
- electric hob
- toasters
- kettles
define direct current (DC)
a steady current, constantly flowing in the same direction in a circuit from positive to negative terminal
what produces direct currents
electric cells or batteries
define alternating current
a current that continuously changes its direction, going back and forth around a circuit
what does an ac power supply have
two identical terminals that change prom positive to negative terminal
how can we know the frequency of an alternating current
knowing the number of times the current changes back and forth each second
what is mains electricity in the uk?
frequency of 50 Hz and potential difference of around 230v
what does a DC graph look like
horizontal line going out of positive
what does an alternating graph look like
wave shape ending underneath
what produces alternating currents
electrical generators ie mains electricity
how to know which fuse to use
must be closest calue above current reqired
which supply needs a transformer
AC supply
how does an earth wire help saferty
- connected to metal casing
- which provides a low resistance path to ground
- if casing becomes live
- theres a large current in the earth wire
- hence fuse breaks
- circuit switches off
whats the purpose of a fuse
- to prevent overheating
- to switch off circuit
- to prevent current exceeding a certain value
how can you test if the fuse is correct
- measue current using ammeter
- vary current using variable resistor
- find a way that the fuse has broken
