Chapter 4 🚨 Flashcards
Do you use ammeters in series or in parallel?
Series
In a parallel circuit, how do you calculate the total current?
The total current is the sum or the currents in the separate sections
In a parallel circuit what is important to remember about the potential difference across each component?
It is the same
In a parallel circuit, bigger the resistance…
The smaller the current
How to calculate current using potential difference and resistance?
Current = potential difference/ resistance
When you add more resistors in a parallel circuit, why does the total resistance decrease?
The total potential difference is the same, so the total current increases. The total resistance = pd/current, so this means the resistance is less
In a series circuit, what is important to remember about the current?
The current passing through each component is the same
How do you calculate the total potential difference of a series circuit?
Add up the potential differences of all the components
How to calculate the total potential difference of cells in a series circuit
Add up the potential difference of each cell
How to find the total resistance in a series circuit?
Add up the resistance of each component
When you add more resistors in a series circuit, why does the overall resistance increase?
The total potential difference is shared across more resistors, giving each one less. This means that the current decreases, and as the total pd doesn’t change, this means that the total resistance is greater than before
How to calculate resistance using pd and current
Resistance = pd/current
What is a diode?
A non ohmic conductor
Only lets current flow in one direction
What is a light emitting diode?
Emits light when current flows through it in a forward direction
What is a thermistor?
Temperature dependent resistor
Resistance decreases when temperature increases
Why are ammeters connected in series?
So the current across them and the component is the same
Is a voltmeter wired in parallel or series?
Parallel
Why is a voltmeter connected in parallel?
So it measures the potential difference across it
What is resistance?
Resistance is when the electrons travelling around the circuit have go push through the ions in the metal filament
How to calculate resistance using potential difference and current
Resistance (ohms) = potential difference/current
What is the current through a resistor directly proportional to?
The potential difference across the resistor
What is Ohm’s law?
The current through a resistor at constant temperature is directly proportional to the potential difference
Function of cell
Pushes electrons around a complete circuit
Function of switch
Enables current to be turned on and off
Function of bulb
To indicate when a current is passing through the circuit
What is an ammeter?
Used to measure electric current
Function of fixed resistor
Limits current in circuit
Function of variable resistor
Allows current to be varied
Function of fuse
Melts to break circuit when current is too high
Function of heater
Used to transfer energy from an electric current to heat surroundings
function of voltmeter
Measures voltage (potential difference)
How to calculate charge flow using current and time
Charge flow = current x time
What is the name for a charged atom?
An ion
What happens when an object becomes charged?
It loses or gains electrons
Which type of forces attract?
Opposites
What is a charged atom called
An ion
How to objects become hatched by friction
Electrons are transferred
Where is an electric field strongest
Nearest to it
Which direction do electric field lines go in
Positive to negative
What happens to cause a spark
When there is a high PD between an object and an earthed object
High PD = strong electric field
This pulls electrons out of air molecules
This makes air conductive so a current can flow through causing a spark
What does the voltage of a battery tell you
How much energy it transfers to each coulomb of charge
What is the direction of current
Positive to negative
Why is a wire an ohmic conductor
It’s resistance stays constant
Why does increased temperature increase resistance
The atoms are vibrating more so they resist the passage of the electrons
Why is a diode a non ohmic conductor
The current isn’t directly proportional to the PD
What happens to the resistance of an LDR if the light intensity increases
It decreases
Where does the current go in a series circuit
Through each component
What happens to the PD in a series circuit
It is shared between the components
What is the total PD of cells in a series circuit
The sum of all the PDs
How to calculate resistance in series
Add the sums of all the resistances together
Why does adding more resistance in series increase the total resistance
The current through the resistors is less and the PD is unchanged
How to find the total current in a parallel circuit
The sum of the currents through the separate branches
What is the PD of components in parallel
The same
How to work out total resistance in parallel
R1 x R2
———
R1 + R2
potential difference of live wire
230 V
potential difference of people
0V
why do you get an electric shock when you touch live wire?
wire = 230 V
we = 0V
large potential difference between us and wire so charge passes through us
What is current?
A flow of electrical charge
What is he potential difference?
The pushing force which drives the charge around the circuit
How does rubbing a rod with a cloth cause it to become charged?
There is friction between the two
This causes electrons to move from the objects
Which leaves the charge on one positive
And the other negative
