Chapter 17 - Household Electricity Flashcards
What is the difference between DC and AC
DC is in one direction
AC is repeatedly reversing its direction
What is the type of current, max and min voltage and frequency in mains electricity?
AC, +325V -325V, 50Hz
What can a diode do to an AC
Can be used for half wave rectification. AC->DC
Where would you measure the peak voltage?
From the peak voltage to zero volts
Why is plastic used as a case for sockets and plugs?
Good insulator and reasonably cheap
What is a mains cable made out of
2 or 3 insulated copper wires surrounded by a layer of plastic material. Wires are Live, Earth and Neutral
In a plug, what wire is the brown wire and where is it in the plug?
Live and on the in right
In a plug, what is the striped yellow and green wire and where is it in the plug?
Earthed wire and at the top
In a plug, what is the blue wire and where is it in the plug?
Neutral and on the left
Why is copper used in the wires of a plug?
Good conductor and bends easily
What does a fuse contain?
A thin wire with a certain resistance
What happens to the wire in a fuse if the current becomes too high?
It heats up, melts and cuts off the current (breaks circuit)
Where is the fuse fitted in the plug?
In series with the live wire
Why is the fuse fitted in series with the live wire?
Because if it blows, the appliance won’t become live from the live wire
What is a circuit breaker?
An electromagnetic switch that opens and breaks the circuit if too much current passes through it
When do you not need to earth an appliance?
When the appliance has a plastic case because plastic is an insulator and can’t become live
Why would you use a circuit breaker over a fuse?
Circuit breakers work faster and can be reset more quickly and conveniently
Why would you use a Residual Current Circuit Breaker over a Circuit Breaker?
RCCB is more sensitive
What is the power supplied to a device
The energy transferred to it every second
What is the potential difference supplied to a device?
Energy transferred to the appliance by each coulomb of charge that flows through it
What is the current supplied to a device?
The charge that flows through it each second
What are the standard fuses for domestic appliances?
3A, 5A, 13A
What happens when an electrical charge flows through a resistor
It heats up due to energy being transferred to the resistor
What does the energy transferred to a resistor depend on?
Amount of charge that passes through it
The P.D across the resistor
What is a Kilowatt-Hour?
The energy supplied to a one kW appliance in 1 hour
Why are electrical faults dangerous?
They can cause fires and electric shocks
What is the National Grid
A network of cables and transformers that distributes electricity
When are step up transformers used?
To raise the power station voltages to grid voltages
When are step down transformers used?
To lower the grid voltage for use in industries and homes
What is the benefit of a high grid voltage?
It reduces the current needed, reducing energy loss, making the system more efficient
