Electricity Flashcards
what is current
the rate of flow of charge
what is potential difference
the work done per unit charge between 2 points
what is 1 coulomb
the amount of charge that passes in 1 second when the current is 1
what type of circuit must the ammeter be attached to get a current reading
An ammeter must always be attached in series
what type of circuit must a voltmeter be attached to get a voltage reading
It must be attached in parallel
what is potential difference between 2 points
The amount of work done moving charge between those points
what is resistance
How difficult it is for current to pass through
What is ohms law
current is directly proportional to the voltage across it
what are ohmic conductors
conductors that follow ohms law
When does Ohms law become true for components
When constant physical factors such as temperature and light remain constant
what does an I-V graph of an ohmic conductor look like
straight line graph going through the origin
what does a lower gradient of a I-V graph mean
there is a greater resitscance
what is a rheostat
a variable resistor used to control current
what is the resistance of a voltmeter
infinite resistance
what is the resistance of an ammeter
0/no resistance
how does heat effect resistance
the particles vibrate more at higher temperatures which makes it harder for electrons to move through the wire
What are diodes
Semi-conductors that only let current flow in one direction
What is forward
The direction in which current is allowed to flow
What is the threshold voltage i
The voltage required for diodes to allow current to flow. (It is normally 0.6V)
Is a filament lamp an ohmic conductor
No it isnt
How can you tell what is or is not an ohmic conductor
The I-V graph needs to be a straight line. If the graph is not a straight line then it is not an ohmic conductor
what is resistivity
It is a measure how much a particular material resists current flow
what is the difference between resistance and resistivity
Resistivity is how much a MATERIAL resists current flow whilst
Resistance is how much an OBJECT resists current.
resistivity is a property of a material while resistance is the property of an object.
What is a semi-conductor
It is a material that doesnt conduct electricity as good as metals because they have fewer electrons
what are 3 common semi-conductor
-thermistor
-diode
-LDR`
what is a thermistor
It is a component where is the temperature is higher the resistance is lower. This is because higher temperature means more electrons escape from their atoms so there will be more charge carriers
what is a LDR
It is a light dependent resistor which means the more light the lower the resistance.
What is a superconductor
A conductor which has 0 resistance
How can you make a super conductor
- By reducing the temperature you can lower the resistance till eventually you get 0 resistance
what is traditional temperature
It is the critical temperature that needs to make a superconductor.
What are 2 uses of a superconductor
- power cables
- creating a strong magnet for medicinal uses
what is power
The rate of energy transfer
What is the equation for energy transfer without using power
E = IVt
energy transfer = current x voltage x time
What is internal resistance
The resistance inside of a battery
What is e.m.f
It it the energy transferred to each electron. e.m.f is measured in volts
What is load resistance
The total external resistance in a circuit (this does not include internal resistance)
What is terminal p.d
The energy transferred when one coulomb of charge flows through the load resistance
what is lost volts
The energy lost in overcoming the internal resistance
what is the equation for e.m.f with lost volts
e.m.f = lost volts+ terminal p.d
what is kirchoffs first law
current entering a junction is equal to current leaving a circuit
what is kirchoffs second law
the total e.m.f is equal to all the p.d of all the components
how do you calculate the total e.m.f of cells in series
You add the e.m.f of all the cells together
how do you calculate the total e.m.f of all cells in parallel
The total e.m.f is the same as the e.m.f of one cell
what are potential divider circuits
circuits which produce an output voltage as a fraction of their input coltage
what are the 3 main reasons for using a potential divider
- to produce a varying potential difference
- to be able to choose a specific potential difference
- to split the potential difference between two components
what is the equation for a potential divider
Vout = (R2/(R1+R2))Vin
what happens when you switch a fixed resistor with a variable resistor like a thermistor
the output voltage will vary
