Electric Circuits Flashcards
What is the purpose of an electric circuit
To transfer energy from the power source to the components where it is converted into useful forms
Why must a circuit be complete
So that the charges are able to travel around the circuit and deliver energy
Current definition
The rate of flow of charge
What is the unit for for current and what apparatus do we use to measure current
Amps
Ammeter
Which circuit is current the same at all points of the circuit and why
Series circuit because the charges can only flow along one path
Why do parallel circuits have varying current
The charges can follow a choice of paths around the circuit
The current spots at a junction and rejoins at a junction do the current into a junction is the same as the current out of the junction
What is conventional current
Electrons flow from the positive terminal to the negative terminal because they didn’t know about electrons
Which way do electrons really flow through the circuit and why
Actually flow from the negative terminal to the positive terminal because the electrons which are negative repel against the negative terminal and are attracted to the positive terminal
Equation for current
Current = charge/ time
What equation links time, current and charge
Current = charge/ time
Time = charge / current
Charge = current x charge
Series circuit (4)
Only have one path
If a component breaks in the circuit the whole circuit turns off
Energy has to be split between each component so light bulbs are dim
Current stays the same though out the circuit
Parallel circuit (4)
Have lots of paths and branches
If a component breaks the circuit still works for the other components
All the energy from one electron can be given to each component, doesn’t need to share, so the bulb is brighter. Each branch receives the same amount of energy per coulomb
Current changes as electrons split off to different branches of the circuit
Advantages to series circuits (3)
Easy to construct
Less wiring to connect more components to the circuit
Whole circuit can be controlled by a switch
Disadvantages of series circuits (2)
Bulbs will be dimmer as energy is being shared
If one component breaks the whole circuit doesn’t work
Advantages of parallel circuits (3)
All the bulbs are brighter as the energy is not being shared
If a component breaks the rest of the circuit still works
Each component can be individually controlled
Disadvantages to parallel circuits (1)
Hard to construct if you want to add another component
Voltage definition
A measure of how much energy is given to or taken away from a coulomb of charge as it passes around a circuit
How is potential difference measured
Using a voltmeter
It is placed in parallel so that energy per coulomb before a component can be compared to after
What other unit can potential difference be measured in
Joules per coulomb
This is because of the equation that links voltage, energy transferred and charge
Equation for voltage
Voltage = energy transferred/ charge
What equation links energy transferred, charge and potential difference
Potential difference = energy transferred/ charge
Energy transferred = potential difference x charge
Charge = energy transferred/ potential difference
What is linked to current and voltage
resistance
What is resistance
A measure of how difficult it is for a current to pass through a component. Resistance is measured in Ohms using an ohmmeter
What is the the equation that links voltage, resistance and current
Voltage = resistance x current
What is the relationship between current and voltage for a resistor
What would the graph look like
As voltage increases, current increases so they have a directly proportional relationship
So if voltage doubles then current doubles
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Straight line with a positive correlation through the origin
What happens to the current and voltage if a component has a higher resistance
There needs to be a higher voltage in order to have the same current pass through the component as it would be harder to get past it as it has a higher resistance
Where does resistance come from
The electron carrying energy collide with the atoms in the component and lose some of their energy causing the atoms in the component to vibrate and heat up
What is the relationship between voltage and current through a metal filament lamp
What would it look like on the graph
Why is this
Voltage and current are not directly proportional
The line is a curved shape on the graph through the origin
To get bigger currents, even larger voltages are needed as more energy is being transferred to heat energy in the lamp
What is the relationship between voltage and current through a diode
What does the graph look like
As voltage increases current also increases however there needs to be high enough voltages to get current as resistance is very very high
Straight horizontal line so current is 0, then smooth curve upwards at higher voltages
Why must voltages be high for current to pass through a diode
And say something about which way current has to flow in a diode
Coulombs of charge need a certain amount of energy to pass through a diode as there is very high resistance
The symbol tells us that current needs to flow the conventional way, this means that current can only flow one way through the diode
Why do thermistors not behave like normal conductors
The resistance of a thermistor decreases as temperature increases as thermistors are made out of semiconductors
