2 ELECTRICITY Flashcards
Unit for current
Ampere (A)
Unit for charge
Coulomb (C)
Unit for energy
Joule (J)
Unit for resistance
Ohm ( X )
Unit for time
Second (s)
Unit for voltage
(V)
Unit for power
Watt (W)
Dangers of electricity
- Electric Shocks
- Electrical fires
- Damage appliances
How does insulation protect the user?
- Plastic coating covers the wires, so no current flows, as plastic is an insulator
- If someone touches it, they don’t get shocked and prevents short circuits
How does double insulation protect the user?
- Appliances with a plastic case and insulated wires
- If a fault occurs inside, there is no orute for the current to take, so no risk of shock
How do fuses protect the user?
- A thin wire in a ceramic case, when current flows through, it heats up
- When current is too high, the wire melts and is ‘blown’
- Breaks the curcuit, os the user is safe, a nd appliance undamaged
How does an earth wire protect user?
- Appliances in metal cases are earthed, and the earth wires connect to the case
- If the live wire cones loose and touches the case, you are at risk of shock
- Earth wire provides a lower resistance route for current, so current flows thorugh the earth wire, not the user
- As resistance is low, a high current flows which breaks the fuse
Advantages of circuit breakers over fuses
- Can be reset - use magnets not wires
- Act quicker than fuses
Charge equation
Charge = current x time
Charge symbol equation
Q = It
What is potential differance
Voltage
Voltage equation
Voltage = Current x Resistance
Voltage symbol equation
V = IR
What is a volt
Joule per coulomb (J/C)
Define current
The rate of flow of charge
Define voltage
The energy transferred per unit charge passed
Energy equation (charge)
Energy = charge x time
Energy equation (triple)
Energy = current x time x voltage
Energy equation (charge) symbol
E = Qt
Energy equation (triple) symbol
E = IVt
Direction of A.C
Constantly changing
Voltage of A.C
Mains electricity - 230V
Direction of D.C
Current only flows one way (conventional)
Voltage of D.C
Low voltage - Batteries and cells
Power equation
Power = Current x Voltage
Power equation symbol
P = IV
Define power
The rate at which electrical energy is transferred
Series circuit:
* Current
* Voltage
* Advantage
* Disadvantage
- Same everywhere
- Split between components
- Longer battery life (Current is lower)
- All off or all out (all bulbs are connected so go out)
Parallel circuit:
* Current
* Voltage
* Advantage
* Disadvantage
- Splits between branches
- Same everywhere
- Switch on/off seperately
- Shorter battery life
Does a resistor obey ohm’s law
Yes - Straight line through origin
Does a filament lamp obey ohm’s law
No
Does a diode obey ohm’s law
No
Reistor, filament lamp, diode - Which way does it conduct
Diode only conducts one way (others both ways)
Describe a resistor IV graph
I directly proportional to V - straight line through origin
Describe a filament lamp IV graph
As voltage increases, current levels off
Describe a diode IV graph
Sharp increase of current, as voltage increases
What direction is convetional current
Positive to negative
What way do electrons flow
Opposite to conventional current
Why can a metal wire conduct electricity
The negatively charged electrons are free to move around the metal
Why do wire heat up, and bulb IV graphs level off?
- As V increases, R increases, I levels off (V=IR)
- The bulb/wire gets hot, and particles in the bulb/wire vibrate more
- This causes more collisons of particles
- So a higher resistance
- Longer wire = more current = more resistance
Does a thermistor obey ohm’s law
No - As temperature increases, resistance decreases
Does a LDR obey ohm’s law
No - as light intensity increases, resistance decreases
How must you connect an ammeter
In series
How must you connect a voltemeter
In parallel
Double insulated symbol
Battery symbol
Voltmeter symbol
Ammeter symbol
Fuse symbol
LED symbol
Diode symbol
LDR symbol
Resistor symbol
Thermistor symbol
Variable resistor symbol
Common insulators
Wood, plastic and glass
Conductor example
Metal
What materials can build up electrostatic charge
Only insulators
How to show electrostatic charge with paper
- Rub a polythene rod with a duster and hold by pieces of paper
- Electron transfer from duster to rod
- Rod is negatively charged
- Paper stick to rod as attracted
How to show electrostatic charge by suspended rods
- Charge a polythene rod by friction and suspend it upside down
- Electron transfer from duster to rod
- Charge an acetate/polythene rod by friction and suspend next to but not touching other rod
- Like charges repel
- Opposite charges attract
Dangers and soloutions to electrostatically refuelling an aircraft
- Body becomes electrostatically charged during flight, as air rubs on fueslarge
- Can cause a spark and explosion
- Earth the aircraft with an earth wire so there is no build up of charge
- No risk of spark or explosion
How do positive and negative electrostatic charges occur
Transfer of electrons
How does electrostatic paint spraying occur, and what are it’s advantages
- Nozzle has positive charge
- Object has negative charge
- Positive paint droplets repel and spread out
- So you get an even coat
- Positive is attracted to negative, so no paint is wasted as it covers all sides
Colour of live wire
Brown
Colour of neutral wire
Blue
Colour of earth wire
Green / Yellow
Job of live wire
High energy
Job of neutral wire
Complete the circuit (return wire)
Job of earth wire
Safety
What side of the plug is the neutral wire
Left
What side of the plug is the live wire
Right
When is an earth wire needed
If the appliance is not double insulated
How to show electrostatic charge by suspended rods
- Charge a polythene rod by friction and suspend it upside down
- Electron transfer from duster to rod
- Charge an acetate/polythene rod by friction and suspend next to but not touching other rod
- Like charges repel
- Opposite charges attract
How must you connect an ammeter
In series
