Electricity Flashcards
What are amperes (A)?
Unit for current (coulombs per second)
What are coulombs (C)?
Unit for charge
1C = 6.25 * 10 to the 18 electrons
What are joules (J)?
Unit for energy
What are ohms (Ω)?
Unit for resistance of a component
What are volts (V)?
Unit for voltage (potential difference)
1V = 1J/C (joule per coulomb)
What are watts (W)?
Unit for power (joules per second)
What is insulation?
When wires are covered by rubber, an insulator.
What is double insulation?
Appliances that have plastic cases without any wires connected to the case, so that the case cannot become live as it is an insulator.
What is earthing?
Earth wires create an escape route for current to flow through if the appliance develops a fault.
If the live wire becomes loose and touches the metal case, a very large current flows through the earth wire, blowing the fuse and creaking the circuit.
What are fuses?
A very thin wire, which melts if the current is too high, breaking the circuit.
Rating in amps tells you the maximum current that can go through.
What are circuit breakers?
An automatic electromagnet switch which breaks the circuit if the current rises over a certain value.
Better than a fuse as it is more sensitive and can be reset.
What do resistors do?
When current flows through, the resistor heats up as electrical energy is transferred to thermal energy. This makes the metal ions vibrate more, making it harder for electrons to find a clear path through.
Relationship between power, current and voltage:
power = current x voltage P = IV
Relationship between energy transferred, current, voltage and time:
energy transferred = voltage x current x time
E = VIt
What is the mains electricity supply in the UK?
230V
Relationship between voltage, current and resistance:
voltage = current x resistance V = IR
Is mains electricity AC or DC?
AC supply (alternating current)
Are cells/batteries AC or DC?
DC supply (direct current)
Properties of a series circuit
Current is the same everywhere
Voltage/potential difference is shared between components
Total resistance is the sum of the resistance of each component
Properties of a parallel circuit
Current is split between branches
Voltage/potential difference is the same on every branch, shared between components on each branch
1/R = 1/R1 + 1/R2
What is voltage/potential difference?
Energy transferred per unit charge
Measured in volts
How does current change as you change the voltage with a wire?
As you increase the voltage, the current increases
Directly proportional
How does current change as you change the voltage with a resistor?
As you increase the voltage, the current increases
Directly proportional
Steeper gradient is higher resistance
Relationship between energy transferred, charge and voltage:
Energy transferred = charge x voltage
E = Q x V
How does current and resistance change as you change the voltage with a filament lamp?
As the voltage increases, the current rapidly increases
As the temperature increases, the resistance (gradient) increases, hence the curve
Curve getting shallower
How does current change as you change the voltage with a diode?
Current only flows in one direction (current only increases in first quadrant)
How does changing resistance affect current?
As resistance increases, current decreases (inversely proportional)
What do LDRs (light dependant resistors) do?
As light intensity increases, they decrease the resistance.
What do thermistors do?
As the temperature increases, they decrease the resistance.
What are LEDs (light-emitting diodes)?
Emit light when current flows through
Don’t have a filament so cannot burn out
What is resistance?
How difficult it is for charge to flow through something
Measured in ohms (Ω)
Insulators have high resistance, conductors have low resistance
What does Ohm’s Law state?
Voltage is directly proportional to current when temperature is constant
V∝I
What is the standard frequency in the UK?
50Hz
What is current?
Rate of flow of charge
Measured in amps (coulombs per second)
Flow of negatively charged electrons
Relationship between charge, current and time:
charge = current x time Q = I x t
Examples of electrical conductors:
All metals
Examples of electrical insulators:
Plastic, wood
What is static electricity?
The build-up of electric charge on an insulated object.
Rubbing polythene and acetate rods with a cloth
Electrons move from the duster to the polythene rod, making the duster +ve and the rod -ve
Electrons move from the acetate rod to the duster, making the rod +ve and the duster -ve.
Using a gold-leaf electroscope
Bring the charged object to the disc of the electroscope
This induces a charge in the metal disc, which induces a charge in the gold leaves
As the gold leaves have the same charge, they will repel eachother.
How does an inkjet printer work:
Uses charged plates to direct a spot of ink onto the pager
