4th - Current And Mains Electricity Flashcards
What is current measured in (amps
Coloumbs per second C/s
What is voltage measured in (volts)
Joule per coloumb J/C
What is power measured in (watt)
Joule per second J/s
How is a frayed cable a hazard
Plastic insulation no longer intact
May be short circuit
- risk of electric shock
- heating and risk of fire
How is long cable a hazard
Long cables have larger resistances
- wire will heat up and cause a fire
How are damaged plugs a hazard
Plastic insulation/ cover is missing/broken
- live wires are exposed
- risk of electric shock
How is water around socket a hazard
Water in electrical equipment, allows electricity to conduct to outside
- cause electric shock
How is pushing metal into sockets a hazard
Metal is a good conductor
- risk of electric shock
What is plug casing made of and why
Plastic - insulator
- current cant pass through
- no risk of electric shock
What is wire covering made of and why
Plastic - insulator
- current cant pass through ]
- no risk of electric shock
- wont short circuit
What are progs made of and why
Brass - conductor
- current easily passes through
- no malleable so prongs wont bend
What are wires made of and why
Copper - good conductor
What colour is the live wire
Brown
What colour is the neutral wire
Blue
What colour is the earth wire
Green and yellow
What is the purpose of the earth wire
To keep user safe form electric shock
Voltage of live wire
Alternates between +230v and -230V
Voltage of neutral wire
0 v
What is the earth wire connected to
The metal casing of the appliance
What happens if the live wire touches the metal casing
- The casing is earthed due to the earth wire
- a big current flows through live wire -> case -> down earth wire
- surge in current melts the fuse -> cuts off the live supply (breaks circuit)
What does fuses prevent
The risk of fire
How should fuses be rated
As near as possible to the current, but just a bit higher than the normal current
What does it mean when an appliance is double insulated
- made of plastic casing, or electrics are completely encased in a plastic cover
- only needs a live and neutral wire
What happens if u pass current through a resistor or wire
Both will heat up
Electrical energy is transferred to heat energy
The metal ions in a fuse is vibrating in position. This means that free ….
Free electrons will collide with the metal ions
And transfer the energy to the lattice in the form of heat
If you increase current enough, what is produced
Heat produced in the wire is enough to melt it
= the fuse has blown
= now safe
Current, voltage, power
Power = current x voltage
Change 100 milli amps to 0.1 amps
What is power
The rate of transfer of energy
Current, voltage, energy transferred, time
Energy transferred = current x voltage x time
Time has to be seconds
What is the difference between a DC and an AC current
DC - current only travels in one direction
AC - current constantly changes direction
What current is a main supply (DC or AC)
AC
- high voltage of 230v
- doesnt need replacing
- not portable
What current is a battery supply (DC or AC)
DC
- low voltage
- needs replacing / recharging
- portable
What does charge need to flow
Potential difference and a complete circuit
What is current
The rate of flow of charge
What is high current
More charge (Q) flowing past a point in a circuit per second
What is low current
Less charge (Q) flowing past a point in a circuit per second
Charge, current, time
Current = charge / time
What is the direction for current
From positive to negative (big line to small line)
Why do bulbs light instantly
Electrons (charge) are found everywhere in a circuit, but the push from the cell makes them move
