Energy and voltage in circuits Flashcards
Name the two ways that electrical components can be joined together
Series and parallel
What is current?
The rate of flow of charge
What is electric current in solid metallic conductors?
A flow of negatively charged electrons
Why is current conserved at a junction in a circuit? And what does this mean?
The charge is conserved
This means that the amount of current flowing into the junction is equal to the amount of current flowing out of it
What is voltage?
The energy transferred per unit charge passed. The volt is a joule per coulomb
What is the voltage across components connected in parallel?
The same
What is the relationship between time, charge and current?
Charge = current x time
Q = I X T
What is the relationship between current, resistance and voltage?
Voltage = current x resistance
V = I x R
Why is a series or parallel circuit more appropriate for particular applications, eg domestic lighting?
Series:
Advantages – all components controlled by a single switch, fewer wires required
Disadvantages – components cannot be controlled separately, if one component breaks all the other components stop working
Parallel:
Advantages – components can be individually controlled using their own switches, if one components breaks then the others will continue to function
Disadvantages – 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
What can be used to indicate the presence of a current in a circuit?
LEDs and lamps as they light up when current flows through them
LED – light-emitting diodes
Voltage in parallel
The total voltage across each branch is the same as the voltage of the power supply
Voltage in series
The total voltage of a power supply is shared between the components
For two identical components (with equal resistance), the voltage across them will be: the same, equal to half the total voltage of the power supply
For two non-identical components (with different values of resistance), the voltage will be: higher across the component with the higher resistance, lower across the component with lower resistance
Current in parallel
Current has different values at different points in the circuit as the current splits at a junction
Therefore, the electrons have different paths they can take
Current in series
The currently has the same value at any point as the electrons only have one path they can take
What does the amount of current flowing in a series circuit depend on?
The voltage of the power source
The number and type of components
How does the voltage of the power source affect the current flowing in a series circuit?
Increasing the voltage of the power source drives more current around the circuit
Decreasing the voltage of the power source reduces the current
How does increasing the number of components in the circuit affect the current flowing in the circuit?
Increasing the number of components increases the total resistance, hence less current flows through the circuit
What is the relationship between voltage, energy transferred and charge?
Energy transferred = charge x voltage
E = Q x V
What do parallel circuits contain?
Junctions and branches
What is a junction?
A point where two or more wires meet to form a new branch
What is a branch?
A connection between components
Resistors in series (total resistance)
When two or more resistors are connected in series, the total resistance is equal to the sum of their individual resistances
What is resistance measured in?
Ohms
What is the total voltage in relation to resistors?
The sum of the outages across each of the individual resistors
Features of parallel circuits (current, voltage and resistance)
The current from the supply splits in the branches
The voltage across each branch is the same
The total resistance is
1/RT = 1/R1 + 1/R2 + 1/R3
Features of series circuits (current, voltage and resistance)
The current is the same at all points and in each component
The voltage of the power supply is shared between the components
The total resistance is the sum of the resistances of each component
What is resistance
The opposition to the flow of current, the higher the resistance of a circuit, the lower the current
What are the types of resistors?
Fixed, variable
Fixed resistors
Have a resistance that remains constant
Variable resistors and how can they be changed?
Can change the resistance by changing the length of wire that makes up the circuit
A longer length of wire has more resistance than a shorter length of wire
How could a student investigate the relationship between current and voltage?
Equipment – ammeter, voltmeter, variable resistor, power source, wires
Filament lamp:
Ammeter, filament lamp and variable resistor in series, voltmeter connected in parallel to the filament lamp
Diode –
Ammeter, diode and resistor connected in series, voltmeter connected in parallel to the diode
Measure the voltage (dependent variable) at each change in current (independent variable)
Or at each change of the voltage at the power source
What is Ohm’s law?
A law that states that the electrical current flowing through any conductor is directly proportional to the potential difference (voltage)
What are linear IV graphs, and what components have them?
Linear (directly proportional) IV graphs are straight lines through the origin
Voltage and current increase/decrease by the same amount
Indicating a constant resistance
Components with linear IV graphs include – fixed resistors, wires (at constant temperature)
What are non-linear IV graphs and what components have them?
Non-linear IV graphs are curved, indicating a variable resistance
Components with non-linear IV graphs include filament lamps, diodes, LDRS, thermistors
What is the IV graph for a filament bulb?
Non-linear/not directly proportional
IV graph is not a straight line – current and voltage do not increase/decrease by the same amount
Slope is not constant – resistance changes
The IV graph for a filament lamp shows that
Current increases at a proportionally slower rate
The resistance increases – the flatter the slope, the higher the resistance
What is a diode?
A diode allows current to flow in one direction only – forward bias
In reverse direction, the diode has very high resistance and no current flows – reverse bias
What is the IV graph for a diode?
When the current is in the direction of the arrowhead symbol, this is forward bias
On the IV graph, this is shown by a sharp increase in voltage and current on the right side of the graph
This shows the resistance is very low
When the diode is switched around, this is reverse bias
On the IV graph, this is shown by a zero reading of current or voltage on the left side of the graph
This shows the resistance is very high
What can influence the resistance of resistors?
Environmental conditions such as temperature and light intensity such as thermistors and light-dependent resistors (LDRs)
What does the resistance of a thermistor depend on?
Its temperature
How does the resistance of the thermistor increase/decrease?
As the temperature increases, the resistance of a thermistor decreases
As the temperature decreases, the resistance of a thermistor increases
What does the resistance of an LDR depend on?
The light intensity on it
How does the resistance of an LDR increase/decrease?
The resistance of an LDR is high in dark conditions and low in bright conditions
As the light intesity increases, the resistance of an LDR decreases
As the light intensity decreases the resistance of an LDR increase
