Fuse
- Stops appliance from working if current get too high
- Current melts fuse wire
Earth wire
Provides an alternative route for current to flow down
Circuit breakers
When a fault occurs, the circuit breaker is tripped, it can then be reset
Double insulation
- No live conductor can tough the outer casing
- Prevents user from getting shocked
Power equation
Power (W) = Current (A) x Voltage (V)
Energy transferred equaitons
Energy transferred (J) = Current (A) x Voltage (V) x Time (s)
Energy transferred (J) = Charge (C) x Voltage (V)
Direct Current (D.C.)
- Only in one direction
- From + to -
- Low voltage appliances can use D.C.
Alternating Current (A.C.)
- Current direction changes
- Potential difference (voltage) changes
- Frequency of 50 Hz
- A.C. current is supplied to buildings
Plugs
- Homes are supplied by A.C. current
- 220V - 240V
Parts: - Live wire: Carries the current
- Neutral wire: Completes the circuit
- Earth wire: Carries no current, there for protection
Series circuit
- Voltage is shared
- Current is constant
Parallel circuit
- Voltage is constant
- Current is shared
Resistance effect
- The higher the resistance the less current flows at a given voltage
Resistance factors
- Lenght of wire: Longer wire = Greater resistance
- Thickness of wire: Smaller diameter = Greater resistance
- Temperature of wire: More temperature = Greater resistance
- Material of wire: Different materials have a different resistance
Heating effect of current and resistance
As current flows through wires and components, those with a larger resitance have an increased temperature
- More resistance = More temperature
- More current = More temperature
Resistance equation
Resistance (Ω) = Voltage (V) / Current (A)
Current
- The rate of flow of charge
Current equation
Current (A) = Charge (C) / Time (s)
Electrostatic electricity formation
- When electrons build up on an insulator, causing an imbalance
- Two insulators are rubbed together. Electrons are transferred between two objects, charging them
Dangers of electrostatic
- Lightning strike -> Death
- Sparks -> Fire
Spray paining
The negatively charge particles of the spary paint get attached to the positively charged frame
Crop spraying
Negatively charged particles in the sparyer repel each other, spreading them appart ensuring and even spred on the crops
Filtering pollutants
- Particles pass through a negatively charged grid. They get negatively charged
- Negatively charged particles get attracted and attach to the postively charged collecting plates
Photocopying
- The image is projected onto a positively charged copying plate
- Where light falls onto the plate, charge leaks
- Negatively charged toner particles are attracted to the remaining positive areas
- Paper is placed over the copying plate. Toner is transferred to the paper and heated to make it stick
