Electric Circuits Flashcards
What is the function of a battery?
To provide power to a circuit
What is a cell?
An energy source for a circuit
What is a battery?
Multiple cells
What is the function of a connecting wire?
To allow electrons to flow
What is the function of a switch?
To “pause” and “restart” the flow of charge
What is the function of a resistor?
To oppose the flow of charge
What is the function of a rheostat?
To allow the resistance to be adjusted
What is another name for a rheostat?
Potentiometer
What is the function of a lightbulb?
To show current in the form of light
What is the function of a LED?
To allow current to flow in one direction
What is the function of an ammeter?
To measure current
What is the function of a voltmeter?
To measure the potential difference in current
What is the difference between emf and potential difference?
Emf is voltage when current is not flowing
Potential difference is voltage when current if flowing
How are pd and emf measured?
In Volts
How should a voltmeter be connected in a circuit?
In parallel
Why does a voltmeter need to be connected in parallel?
It has a high resistance
If it were connected in series, it would serve as another resistor
This would affect the reading
What is current?
The number of coulombs of charge that flow past a point in the circuit every second
What are the two requirements for charges to be able to flow in a circuit?
There must be no breaks in the circuit
The charges must have energy to be able to move
What is the definition of current?
The rate of flow of charge
What is the symbol for current?
I
What is the measurement of current?
Ampere
What is one ampere?
One coulomb that flows past a certain point in one second
What is the equation for current?
Current is equal to charge over time
Q
I = —
Δt
What is the conventional flow of current?
From the positive terminal of a battery to the negative terminal of a battery
How is the direction of current shown?
Using arrowheads
What instrument is used to measure current?
An ammeter
How is an ammeter connected to a circuit?
In series
Why can an ammeter be connected in series?
It has a very low resistance
It does not decrease the current in a circuit
What is the definition of resistance?
The property of a material which causes it to oppose the flow of charge through it
When can resistance be a detriment?
When current does not need to be opposed
Give an example of when resistance is detrimental
High voltage transmission lines
If there is too much resistance, they heat up
This causes energy to be lost to the environment
When can resistance be useful?
When the heat or light energy that resistors cause to be released is needed
Give two examples of where resistance is useful
Heating elements
In electronics
How can resistance be useful in electronics?
It restricts the flow of current to other components, thereby protecting them
How do reinstalls cause things to heat up?
Electrons bump into the particles of the resistor
Kinetic energy is transferred
Raises the temperature of the resistor
What is the formula for resistance?
Resistance is equal to voltage over current
V
R = —
I
What is the relationship between resistance and voltage?
Directly proportional
As the one increases, so does the other
What is the relationship between resistance and current?
Inversely proportional
As the one increases, the other decreases
What is the unit of measurement for resistance?
The ohm
What is the symbol for an ohm?
Ω
What is an ohm?
One volt per ampere
What four factors affect resistance?
Length
Thickness or cross-sectional area
Temperature
Type of material
How does length affect resistance?
The greater the length of a resistor, the more resistance it has
How does thickness or cross-sectional area affect resistance?
The greater the cross-sectional area of a resistor, the smaller its resistance
How does temperature affect resistance?
The higher the temperature of a resistor, the greater its resistance
How does the type of material affect resistance?
The greater the resistivity of a metal, the greater its resistance
What does “resistors connected in series” mean?
There is only one path along which the current can flow
What does mean to have “resistors connected in parallel”?
There is more than one path along which current can flow
How is current affected when resistors are connected in series?
The more resistors there are, the slower the current flows. However, current is equal across all of the resistors
What is the formula for finding the equivalent resistance of resistors connected in series?
Rtotal = r1 + r2 …
How is voltage affected by resistors connected in series?
It is divided
The amount of voltage in one resistor is proportional to the a,punt of resistance it offers
What results in a potential difference across a resistor?
Energy is transferred as it passes through the resistor
The decrease in potential electrical energy results in a potential difference across the resistor
What is equivalent resistance in a parallel circuit like?
It is smaller than the resistance of lowest resistor in the set
How is equivalent resistance in a parallel circuit calculated?
1 1 1 1
– = – + – + – …
Rp r1 r2 r3
How is current affected when resistors are connected in parallel?
It is divided
The sum of the current in the branches is equal to the total current in the circuit
How is potential difference affected by resistors in parallel?
It is equal to the potential resistance across the whole combination
How do cells work?
They convert chemical potential energy into electrical energy
What are the three common components in a cell?
Positive electrode
Electrolyte
Negative electrode
What form is the electrolyte in a cell?
It can be a liquid, paste or a powder
What is the electrolyte in an alkaline cell?
Potassium hydroxide
What does the negative terminal of an alkaline cell consist of?
Zinc powder
What does the positive terminal of an alkaline cell consist of?
Manganese dioxide
What happens when this alkaline cell is in use?
The manganese dioxide is converted into manganese oxide and hydroxide ions
These ions react with the zinc metal
This forms zinc oxide, water and electrons
What constitutes an electric current?
Moving charges
When is a cell said to be flat?
When too few electrons are being generated
What causes a cell to go flat?
The manganese oxide has been almost used up
