Topic 2 Electricity Flashcards
Total resistance =
R1 + R2 etc.
What colour is the earth wire and what does it do?
Green and yellow, safety wire to stop the appliance becoming live, at 0V if running smoothly
What colour is the neutral wire and what does it do?
Blue, completes the circuit, around 0V
What colour is the live wire and what does it do?
Brown, carries the alternating potential difference from the supply, p.d. between live and earth wire is 230V
What is the cells function and symbol? 1
pushes the electrons around a complete circuit
What is the switches function and symbol? 2
enables the current to be switched on or off
What is the bulb/lamps function and symbol? 3
emits light
What is the fixed resistors function and symbol? 4
limits the current in a circuit
What is the variable resistors function and symbol? 5
allows current to be varied
What is the fuses function and symbol? 6
will melt and break if the current is too strong
What is the diodes function and symbol? 7
allows current in only one direction
What is the LEDs function and symbol? 8
emits light
What is the LDRs function and symbol? 9
decreases in resistance as light intensity increases
What is the thermistors function and symbol? 10
resistance depends on temperature
What is the ammeters function and symbol? 11
measures flow of electrons (current)
What is the voltmeters function and symbol? 12
measures electric potential difference (voltage)
Define current
Current is the rate of flow of charge
Charge is measured in …
Coulombs (C)
Current is measured in …
Ampere (A)
Potential difference is measured in …
Volts (V)
Resistance is measured in …
Ohms (Ω)
What is ohm’s law?
Ohm’s law states that the current flowing through a wire is directly proportional to the voltage across it (if the temp remains constant)
Define resistance
It is a measure of the opposition to the current flow in an electrical circuit
As length of wire increases, potential difference _________, current __________ and resistance ________.
increases, decreases, increases
Describe the I-V graph of a resistor
13, the current is directly proportional to the potential difference so you get a straight line
Describe the I-V graph of a bulb/filament lamp
14, current and p.d are proportional to begin with - as the current increases, the temp increases and so the resistance increases. This means less current can flow so the graph curves and plateaus.
Describe the I-V graph of a diode
15, the current will only flow in one direction so the diode has a very high resistance in one direction.
Describe the LDR graph
16, the darker it is, the more resistance there is
Describe the Thermistor graph
17, the colder it is, the more resistance there is
What are the three golden rules for series circuits?
-current is the same throughout
-potential difference of the power supply is shared between the components
-resistance is added up, Rtotal = R1 + R2
Define potential difference/voltage
the difference in electrical potential between two points, the driving force that pushes electric charge around a circuit
What are the three golden rules for a parallel circuit?
-current will be shared through separate components
-p.d. is the same across each component
-adding a resistor in parallel reduces the total resistance
What is AC?
Alternating current - the current is constantly changing direction
What is DC?
Direct current - the current only flows in one direction
Is the electricity in your home AC or DC?
Alternating current (AC)
What is the supply and frequency of the current in the mains supply?
230V, 50Hz
What type of current to cells and batteries supply?
Direct current (DC)
What is meant by 1 Amp in terms of charge?
1 coulomb of charge flows past a point every second
What is meant by 1 Volt in terms of charge?
1 joule of work is done per coulomb of charge
Define a transformer
Increase and decrease voltage at particular stages in the National Grid
Describe how step-up transformers are used in the National Grid system
A step-up transformer is used after the power station to increase the potential difference which then in turn decreases the current. This means less energy is wasted through thermal heat so it improves efficiency.
Describe how step-down transformers are used in the National Grid system
Step-down transformers are used to bring the voltage back down to 230V so it is safe to use at home
Like charges ______
repel
Unlike charges ______
attract
Insulating materials that lose electrons when rubbed become __________ charged
positively
Insulating materials that gain electrons when rubbed become __________ charged
negatively
Explain why insulators don’t lose their charge
The electrons gained by the insulator are held by the atoms. It doesn’t conduct electricity so the electrons can’t leave
Electric field lines go from …
positive to negative
Explain how an uncharged object may become positively charged
- negatively charged
- electrons are transferred
- from the neutral object
How are sparks caused?
When there is high p.d. between a charged object and the earth
