Currents Flashcards
What does AC stand for
Alternating current
How to calculate T (time period), what is it?
Time taken to complete 1 full cycle
T = 1/f
f = 1/T
Time = s
f = Hz or S-1
What do AC currents do
Change direction many times per second
What type of current is mains electricity? What’s its average and peak?
AC
UK mains averages at +- 230V
Peaks at +- 325V
Power =
Work done/ Time
Current x p.d
P= I x V
W= A x V
What does DC stand for
Direct current
Why do we say 230V is the UK mains
The power supplied it equivalent to a 230V battery
What do DC currents do?
What produces this type of current?
Don’t change direction
Batteries
AC has a frequency, what does that mean? What is the UK mains frequency?
No. Times the current changes direction per second
50Hz
Describe the axis for oscilloscopes
X axis is time
Y axis is potential difference
What are the 7 parts of a plug
- Earth wire (yellow and green)
- Neutral wire (blue)
- Cable grip
- LIVE wire (brown)
- Fuse
- Outer case
- Pin
What are the pins in a plug made of? Why?
Brass
Good conductor
Won’t bend
Doesn’t oxidise
What are the wires in a plug made of? Why?
Copper
Soft plastic
Good conductor
Flexible
Insulates
Flexible
What is the case in a plug made of? Why?
Hard plastic
Insulates
Rigid (keeps its shape)
What is the cable grip in a plug made of? Why?
Hard plastic
Holds wires in place (rigid)
🔳 what does this symbol mean
The device is double insulated
This means that the device has at least two non conductive layers of material between the user and the live current
What are the three pasts of a fuse
Thin metal wire
Insulator case
Metal contacts
How does a fuse keep us safe
If there is too much current the wire will heat up and melt.
This means we have an open circuit so the current can’t flow.
How to choose a fuse
The fuse with the smallest fuse rating that is larger than the current
Why it’s important to choose the right fuse
If the fuse is too small the wire will melt as soon as you turn the device on
If it’s too big the fuse wire won’t melt before a fire starts
Describe the voltage of the different wires
Live wire : 230V
Earth wire : 0V
Neutral wire : 0V (completes the circuit)
