P2.4 Using mains electricity safety and the power of electrical appliances Flashcards
What current do cells and batteries supply?
Current that always passes in the same direction, this is called direct current
What is an alternating current?
One that is constantly changing direction
What is the period of an AC supply?
The time taken for one complete oscillation. You can find the period by looking at the time taken between one peak/trough and the next
What is the frequency of an AC supply?
The number of oscillation per second. You can find it by dividing one by the period
What is an example of an AC supply?
Mains electricity
What frequency does the UK mains electricity have and what voltage?
Frequency of 50 cycle per second (50 hertz) and is about 230 V
How are most electrical appliances connected to the mains?
Using cable and a three pin plug
How many wires does a cable have?
Two or three
What is the core in a cable made of?
Copper, it is good at conducting electricity
What are the outer layers made up of?
Flexible plastic, because plastic is a good electrical insulator
What is the blue wire?
The neutral wire
What is the brown wire?
The live wire
What is the green and yellow striped wire?
The earth wire
What is the case of a plug made up of?
Tough plastic or rubber, good electrical insulators
What are the three pins made up of?
Brass, good electrical conductor
What is there between the live terminal and the live pin?
A fuse
What is a fuse?
A fuse breaks the circuit if too much current flows
What is the cable secured in the plug by?
A cable grip
Where does the blue wire go?
The bLue wire goes to the left
Where does the brown wire go?
The bRown wire goes to the right
Where does the striped wire go?
The sTriped wire goes to the top
If an electrical fault causes too great a current, what happens?
The circuit is disconnected by a fuse or a circuit breaker in the live wire
When the current in a fuse wire exceeds the rating of the fuse it will…
Melt, breaking the circuit
What are some circuits protected by?
Residual Current Circuit Breakers (RCCB)s
How do RCCBs operate?
By detecting a difference in the current between the live wire and neutral wires
RCCBs operate much…
Faster than a fuse
What are appliances with metal cases often?
Earthed
Appliances without a earth wire are what instead?
Double insulated
What do the earth wire and the fuse do together?
Protect the circuit
What are the most common fuse ratings?
3A, 5A and 13A
The thicker the wire in the fuse…
The higher the fuses rating
What happens when an electrical charge flows through a resistor?
It gets hot
A lot of energy is lost in filament bulbs by…
Heating
Less energy is wasted in power saving lamps such as…
Compact Fluorescent Lamps (CFLs)
What is power?
The rate at which energy is transferred by an appliance
What is the equation for power?
E
P = —–
t
What is power measured in?
Watts
What does the P stand for?
Power
What does the E stand for?
Energy
What does the t stand for?
Time
What is the equation for power, potential difference and current?
P = I x V
What does the I stand for?
Current
What does the V stand for?
Potential difference
What is current measured in?
Amps
What is the potential difference measured in?
Volts
Through calculating the current of an appliance what can we determine?
The size of fuse needed
What is the equation for energy transferred, potential difference and charge?
E = V x Q
What does Q stand for
Charge
What is charge measured in?
Coulombs
