Mains electricity Flashcards
How does the use of insulation protects a device?
To prevent electric shocks
What is double insulation?
The appliance has insulation around both casing and around the cables.
What is earthing?
Provides a path for a conductor pathway for excess charges to flow safely away to the ground.
Explain how a fuse protects a circuit
If a dangerously large current starts to flow in a circuit, the fuse will overheat and melt, causing a break in the circuit.
What happens to the temperature of wire when a current is put through it?
The temperature increases
Equation for Power current and voltage is…
Power = current x voltage
What is the use of a circuit breaker?
They automatically switch off the circuit when they detect an overload or short circuit.
Current in a resistor
Causes electrical energy to be transferred as heat, increasing temperature. Used in devices like heaters and toasters.
Energy transfer formula
Energy transferred = current x voltage x time OR Energy transferred = charge x voltage
Alternating Current
This is current flowing in different directions continuously.
Direct Current
This is current flowing in the same direction.
Series Circuits
Components connected end-to-end, same current flows through all component.
Parallel circuits
Components connected across common points, each component gets the full voltage. Ideal for domestic lighting as each light operates independently.
Current in a series circuit
Current depends on the applied voltage and the total resistance.
Voltage in a parallel circuit
Voltage is the same across all branches, current divides among the branches.
Current and voltage are what?
Proportional to each other during fixed resistors
What is ohm’s law and what follows it?
ohm’s law is that for a component at constant temperature, voltage is proportional to current. Resistors follow ohm’s law.
Metal filament lamps
Don’t follow ohm’s law. Resistance increases with temperature.
Diodes
Allow current to flow in one direction only.
Explain why parallel circuits are more suitable for use in the home
As you can turn the lights on/off individually.
Line going through graph for a resistor
Straight diagonal line
Line going through for a filament lamp
Flat S shape but look at revision
Line going through for a diode
Look at revision
What is the definition of voltage
The energy transferred per unit of charge passed.
What is the definition of volt
A joule per coulomb
Why is current conserved at a junction in a circuit?
As charge can not be created or destroyed
What is used to indicate the presence of current in a circuit?
LED’s and lamps
Describe the qualitative effect of changing resistance on the current in a circuit
Increasing the current decreases resistance and decreasing the current increases the resistance
Describe the qualitative variation of resistance of LDR’s with illumination and thermistors with temperature
The resistance of an LDR decreases with increasing illumination, while the resistance of a thermistor decreases with increasing temperature.
Current definition
The rate of flow of charge
What is electric current in solid metallic conductors?
A flow of negatively charged electrons
What is the voltage across two components that are parallel to each other
The same
How can insulating materials be charged by friction?
Rubbing transfers electrons from one material to the other, creating opposite charges
Voltmeters - series or parallel
Parallel
Ammeters - series or parallel
Series
Uses of electrostatic charges
Photocopiers and inkjet printers
Fuelling aircraft
As electrostatic charges may create sparks when refuelling so for safety that it needs to be earthed.
