p5 Flashcards
what is direct current
current that passes round the circuit in one direction only
what is alternating current
current from the mains supply repeatedly reverses direction in. a circuit
what is the frequency of the uk mains supply
50Hz which means that the current reverses itself 50 times each second
what is the equation for alternating frequency
1 / time taken for one cycle
how does the mains supply alternate its current
a live wire alternates between a positive and negative p[otential difference.
how many volts does the live wire alternate between
-325V and 325V
what is the national grid
a system of cables and transformers linking power stations to consumers
what is a step up transformer
used to increase the p.d from the power station to transmission cables
what is a step down transformer
used to decrease p.d to a much lower value for domestic use
what is the outer cover of a three pin plug made from
stiff plastic material that is a good insulator
what are the pins of the plug made from
brass as its a good electrical conductor and is hard and will not rust or oxidise
what is the earth wire ( tree and yellow ) connected to
earth pin
what is the live wire ( brown ) connected to
live pin
what is the neutral wire ( blue ) connected to
neutral pin
what are the outer coverings of the wire made of
flexible plastic material
why is the outer coverings of a wire made of flexible plastic wire
it is a good insulator and can be bent
what does a fuse do
if the current in the fuse becomes too big, it will melt and cut of current to the live wire
why must appliances with a metal case be earthed
the case is attached to the earth wire in the cable, which stops the metal case becoming live if the wire breaks.
why are somer cables thicker than others
the larger the current, the thicker the cable
