Chapter 5 Electricity in the Home Flashcards
What is an alternating current (a.c.)?
An electric current in a circuit that repeatedly reverses its direction
What is a direct current (d.c.)?
An electric current in a circuit that is in one direction only
What is an earth wire?
The wire in a mains cable used to connect the metal case of an appliance to earth
What does a fuse do?
A fuse contains a thin wire that melts and cuts the current off if too much current passes through it.
What is a live wire?
The mains wire that has a voltage that alternates in voltage (between +325V and -325V in Europe)
What is a neutral wire?
The wire of a mains circuit that is earthed at the local substation so its potential is close to zero
What is a oscilloscope?
A device used to display the shape of an electrical wave
What is a plug used for?
A plug has an insulates case and is used to connect the cable from an appliance to a socket.
What are step-down transformers?
An electrical device used to step-down the size of an alternating potential difference
What are step-up transformers?
An electrical device used to step-up the size of an alternating potential difference
What is a three-pin plug?
A three-pin plug has a live pin, a neutral pin and an earth pin.
What is the power grid?
The Power Grid is how the electricity gets to the homes
Mains supply is DC or AC
Battery supply is DC or AC
ac
dc
What is the frequency of the ac mains supply?
50 cycles per second or 50HZ (hertz)
Every mains circuit has a _________ wire and a __________wire
live
neutral
The oscilloscope is used to display the potential difference of an alternating potential difference supply unit . How would the trace change if THE POTENTIAL DIFFERENCE IS INCREASED
waves taller
as amplitude increases
The oscilloscope is used to display the potential difference of an alternating potential difference supply unit . How would the trace change if THE FREQUENCY IS INCREASED
waves closer together
as time for each cycle is less
Give a reason why a mains appliance with metal case is unsafe if the case is not earthed
if live wire touches case, case becomes live
anyone touching case electrocuted as electric current passes through their body to earth
Write the colour of each wire in a mains circuit
live: brown, neutral: blue, earth: green and yellow
Why are the wall sockets in a room connected in parallel with each other
so any appliance connected to wall socket can be switched on or off, without affecting any appliance connected to a different wall socket
A small hairdryer has a double- insulated plastic case and is fitted with a plastic mains cable that contains two wires that are insulated separately. Name the two wires?
Why are the two wires in the cable insulated separately?
the live wire and the neutral wire
the live wire is at 230 V and the neutral wire is approximately at 0 V
they are insulated from each other to stop the metal of the wires making contact
if this happened, a very large current would pass between the wires and the heating effect would cause a fire.
describe the National Grid
- a system of cables and transformers
- a system linking power stations to houses
Describe the difference between a step up and step down transformer
a step-up transformer increases the size of an alternating
potential difference
a step-down transformer decreases the size of an
alternating potential difference
What is the advantage of having a step up transformer in a system? 3 marks
with a step-up transformer between the power station and
the grid cables, power is transferred much more efficiently than if the transformer was not included.
This is because the greater the potential difference is, the smaller the current in the cables is so the smaller the resistance.
heating effect of the current in the cables is for the same
amount of power transferred.
What is meant when something is said to be double insulated?
the outer case of the appliance is made of plastic
and the wires inside are covered in plastic
Why might a person get an electric shock if the cables in a electric mower get cut whilst mowing?
-the live wire is still live with a potential difference of 230 volts
-the human body is at earth potential difference of 0 volts
-therefore if the gardener touches the live wire an electric
current will flow through him to earth
What does an electricity meter measure?
how much energy is supplied
When charge flows through a resistor, energy is transferred to the ____________, so the resistor becomes HOTTER/COLDER
resistor
hotter
Why is copper used for wires?
- good electrical conductor
- bends easily
What wires are inside a three-pin plug
-earth
-live
-neutral
and a fuse
