Topic 2 - Electricity Flashcards
REMINDER - memorise circuit symbols.
Memorise :)
What is the definition for current?
Current is the flow of electrons. It is measured in Amps(A)
How are ammeters connected up into a circuit?
Ammeters are connected up in series.
What is the defintion for potential difference? (voltage)
THe driving force that pushes the charge around a circuit. Measured in Volts.
How are voltmeters connected up into a circuit
They are connected up in parallel
What does a voltmeter measure?
A voltmeter measures the difference in the energy of electrons entering a component and the energy of electrons leaving. i.e Potential Difference
What is the unit for Charge?
Coulomb (C)
What is Charge?
Charge is a property of a body which experiences a force in an electric field.
What is the unit of resistance?
Ohms(Ω)
What is resistance?
Resistance is opposition to the flow of current. Electrons collide with atoms.
What 4 factors affect resistance?
1.Temperature
2.Length
3.Width
4.Material
Diodes allow current to flow in both directions true or false?
False - Diodes only allow current to flow in one direction. A diode in the wrong direction has a huge resistance.
Go Revise I/V Graphs - Diode
Now.
Finish the sentence - Voltage across an ohmic conductor/resistor kept at constant temperature is ….
Voltage across an ohmic conductor/ resistor kept at a constant temperature is directly proportional to the current flowing through it.
What is an Ohmic conductor?
Any conductor which follows Ohms law
Go revise I/V graphs - resistor!
Now.
Go revise I/V graphs - filament lamp!
Now.
What is the rule for current in a series circuit?
In a series, current flowing is the same at all places.
What is the rule for voltage in a series?
In a series, the voltage across each component adds up to the total voltage of the circuit.
What is the rule for current in a parallel circuit?
In a parallel the sum of the currents flowing through the parallel branches equals the current of the whole circuit.
What is the rule for voltage in a parallel circuit?
In a parallel, every branch has the same voltage as the power supply/cell.
What is the rule for resistance in a series?
In a series, the total resistance is the sum of the resistance of every component.
What is the rule for resistance in a parallel?
In a parallel, the more resistors added in parallel the total resistance decreases.
Resistance of a parallel is always LESS than the LOWEST value resistor.
What does a thermistor do?
As temperature increases, resistance decreases.
What does an LDR do?
As light intensity increases, resistance decreases,
What happens when a current is AC?
In AC, the current is constantly changing direction.
How are Alternating Currents produced?
ACs are produced by alternating voltages, in which the positve and negative ends keep alternating.
What is the frequency of UK mains?
50Hz
What are the 3 core cables.
- Brown - live wire 230V
- Blue - netral wire 0V
- Green and Yellow - Earth wire 0V
What voltage is UK mains
230V
What does the earth wire do?
The earth wire carries current away from the appliance casing, in case that the live wire comes loose.
What is the difference between the earth pin vs the live and neutral pins?
The earth pin is slightly longer.
What is power??
Power is the rate at which energy is transferred.
What is the equation for power loss?
Power loss = current^2 x resistance
OR
Power loss = voltage x current
What are the steps of how power gets from the power station to your home?
- 25,000V from the power station passes through a step up transformer up to 400,000V.
- This is to keep current low, so that power loss is low
- The electricity then reaches a step down transformer, which lowers the voltage to 230V
- It then goes to peoples homes.
What is static electricity caused by?
Static electricity is caused by the friction between 2 insulators, which causes electrons to be transferred from one to the other.
What is an electric field?
An electric field is an invisible force around charged objects, it can attract or repel depending on the charge of another object.
What does an electric field look like?
The electric field lines go from positive to negative, and get closer together, the nearer the lines are to the negative/positve charge point.
