2 Electricity Flashcards
Double Insulation
Class 2 appliances have metal cases
Plastic is an insulator so no earth wire
Example: hairdryer
Fuses and Circuit Breakers
- Fault occurs (live wire touches metal case)
- Large current flows down to earth wire and melts fuse
- Fuse breaks, disconnecting the live supply
Current
The rate of flow of charge
What is the conventional current?
- Opposite of ACTUAL current
- Goes from + to -
Voltage
energy lost or gained by each Coulomb as it moves around the circuit
Kirchoff’s Law
Total current entering a junction = Total current leaving a junction
Different types of circuit
- Series
- Parallel
Series Circuit
Current is the same throughout
Voltage is shared between components
Single Loop
Parallel Circuit
Share of current for each loop
Voltage is same throughout (for each loop)
Multiple Loops
Advantages of Parallel Circuit
If one component fails, other components are unaffected
Individual control over each component or loop/components work independently
Disadvantages of Series Circuit
If one component fails, whole circuit is disconnected
Resistance
Opposition to the flow of charge due to collisions between electrons (moving) and nuclei (stationary)
How can the resistance of a conductor be increased?
- Reduce cross-sectional area
- Increase length
What can be used to indicate the presence of a current in a circuit?
Lamp or LED
Relationship with voltage and current in a resistor(Ohms Law)
The current is directly proportional to the voltage, provided that the temperature is constant
Relationship between voltage and current in a filament lamp
As voltage + current increase, so does resistance.
Due to nuclei vibrating more making it more difficult for electrons to pass through.
Diode
Electrical equivalent of a 1 way valve (only lets current flow in 1 direction)
Graph for Diode (Voltage and current)
Peaks as soon as voltage is positive
LDR graph (brightness and resistance)
Inversely proportional
Uses of LDR
Screen brightness on electronic devices
Thermistor graph (temperature and resistance)
Inversely proportional
Alternating Current (a.c)
Voltage continuously changes from + to -
Example of alternating current
Mains electricity
Direct Current (d.c)
Voltage is always positive
Example of Direct Current
Cell
Wires in a plug
- Live
- Neutral
- Earth
Colours of wires in plug: Live
Brown
Colours of wires in plug: Neutral
Blue
Colours of wires in plug: Earth
Green/yellow
Plugs: Live
Alternates between + and - voltages, as electrons are pushed around the circuit
Plugs: Neutral
Stays at 0V, but carries same current as live
Plugs: Earth
Stays at 0V, and doesn’t carry a current unless there is a fault
Examples of electrical hazards
Frayed cables
Water around plugs
Damaged plugs
Voltage of Mains electricity
230V
Practical: investigate how insulating materials can be charged by friction
Rub duster on polythene rod
Polythene rod becomes positive
Duster becomes negative
Due to transfer of electrons
Uses of electrostatic charges
- Photocopiers
- Inkjet printers
Uses of electrostatic charges: Photocopiers
- A copying plate is electrically charges
- An image of the page wanting to be copied is projected on the plate
- Where light falls on the plate, electrical charge leaks away
- The parts charges attract a black powder
- The powder is transferred to paper
- Paper is heated to make powder stick
Dangers of electrostatics
- Lightning
- Fuelling
Dangers of electrostatics: Lightning
- Negative cloud with excess electrons
- Excess electrons flow to Earth as lightning
- Building have lightning conductors to carry this to the ground to avoid damage to building
Dangers of electrostatics: Refuelling
- As fuel rubs against the hose, a static charge can build up.
- If these excess electrons spark across the gap, an explosion can result
- Bending wire allows the electrons to safely cross the gap
