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Electric current is
The rate of flow of electric charge
current units
Amperes (amps) A
What is an amp equivalent to?
Charge of 1 coulomb flowing in one second
How to measure current
Ammeter in series with the component being measured
What are wires of a circuit made of?
Metal- good conductor of electric current
What is a current in solid metallic conductors ?
A flow of negatively charged electrons
What is the equation for charge?
Charge (C) = current (A) x time (s)
Voltage
The energy transferred per unit charge passing between two points
Voltage units
Volts/V
What is a volt equivalent to?
1 joule of energy per 1 coulomb of charge
how to measure voltage
voltmeter connected in parallel with component being measured
Equation for energy transferred
Energy transferred (J)= charge (C) x voltage (V)
Resistance
The opposition of a component to the flow of electric current through it
Resistance units
Ohms (Ω)
What is a resistance of 1 ohm equivalent to?
A voltage across a component of 1V which produces a current or 1A through it
What does resistance control?
The size of the current in a circuit
What does a higher resistance mean?
The smaller the current
What does a lower resistance mean?
The higher the current
Why is copper a good conductor of electricity?
Allows electrons to move more freely/ low resistance
Equation for voltage
voltage (V) = current (A) x resistance (ohms)
What is a series circuit?
A circuit that has only one path for the electrons to take/electric current to flow
Explain current in a series circuit
current has same value at any point, as electrons only have one path they can take
all components in a series circuit have same current
What affects current in a series circuit?
voltage of power source: increasing voltage means more current driven, vice versa
number and type of components, increasing num of components increases resistance + decreases current
What is a parallel circuit?
a circuit that has two or more loops, or more than one path that electrons can take/current can flow
parallel circuits contain junctions (points where two or more wires meet to form a new branch) and branches (sections of wire between junctions)
Explain current in a parallel circuit
diff values at diff points in the circuit as current splits at a junction, therefore, electrons have diff paths they can take
sum of current in individual branches is equal to the total current before and after the branches
What happens at a junction?
Current is always conserved but does not always split equally
Why is current conserved at a junction in a circuit?
because charge is always conserved
Explain voltage in series circuits
total voltage of power supply is shared between the components
for two components w same resistance, voltage will be: the same, equal to half total voltage or power supply)
for two components w different values of resistance, voltage will be higher across component w higher resistance + lower across component w lower resistance
Explain voltage in parallel circuits
The total voltage across each branch is the same as the voltage of the power supply
Advantages of a series circuit
All of the components are controlled by a single switch
Fewer wires are required (cheaper, easier to install)
Disadvantages of a series circuit
The components cannot be controlled separately
if component breaks, all other components stop working
Advantages of a parallel circuit
-The components can be individually controlled using their own switches
If one component breaks, then the others will continue to function
Disadvantages of a parallel circuit
Many more wires are involved which can be more complicated to set up
All branches have the same voltage as the supply making it more difficult to control the voltage across individual components
Explain resistors in series circuits
when two or more resistors are connected in series, total resistance is equal to sum of individual resistances
increasing num of resistors increases overall resistance
total voltage is sun of voltages across of each of the individual resistors
Explain resistors in parallel circuits
In a parallel circuit, net resistance decreases as more components/resistors are added, because there are more paths for the current to pass through.
The two resistors have the same potential difference across them. The current through them will be different if they have different resistances.
increasing number of resistors in parallel—> decrease in resistance—>increase in current
What is an IV graph?
The graph to show how the current varies with voltage for a component
IV graph for a wire or a resistor
relationship between current and voltage for a wire or fixed resistor is linear, or directly proportional
IV graph is a straight line, so voltage and current increase (or decrease) by same amount
slope of the graph is constant, so resistance is constant
IV graph for filament bulb/lamp
relationship between current and voltage for a filament lamp is non-linear/ directly proportional
IV graph is not a straight line, so voltage and current do not increase (or decrease) by same amount
slope of the graph not constant, so resistance changes
IV graph for a filament lamp shows as voltage increases, current increases at a proportionally slower rate and resistance increases; flatter the slope, higher the resistance
IV graph for a diode
diode only allows current to flow in one direction (forward bias)
in reverse direction, diode has very high resistance no no current flows (reverse bias)
How to investigate the relationship between current and voltage experimentally- equipment
Needs:
ammeter: to measure current through component
voltmeter: to measure collage across component
variable resistor: to vary current through circuit
power source: to provide source of potential diff/ voltage
wires: to connect components together
How to investigate the relationship between current and voltage experimentally- variables
Independent variable: current
variable resistor is used to change current flowing through the filament lamp/diode Dependent variable: voltage
voltmeter is used to measure voltage across filament lamp/diode
recording measurements of current + voltage as current increases enables an IV graph to be plotted for each component
What are the two types of resistors?
Fixed resistor: resistance that remains constant
Variable resistor: can change resistance by changing length of wire that makes up the circuit (longer= more resistance) examples are thermistors + light variable resistors
Explain how thermistors work
resistance depends on temp
resistance is high in cold conditions
resistance is low in hot conditions
relationship between temperature and resistance is inversely proportional
Explain how light-dependent resistors (LDRs) work
resistance is dependent on light intensity
resistance of LDR is high in dark conditions
resistance of LDR is low in bright conditions
why can lamps and LEDs be used to indicate the presence of a current?
lamps light up when a current flows in a circuit
LEDs light up when a current flows in a circuit
since both electrical components have a visual response to current, they can be used to indicate the presence of a current in a circuit
What are LEDs?
a type of light emitting diodes
they only allow current to flow through them in one direction
in a circuit, an LED will only light up if placed in correct direction
Note 
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