Electricity Flashcards
What is current?
The rate of flow of charge
Where does an ammeter go and why?
In series due to having a negligible resistance
What is the formula for current?
I = Q/t
What is potential difference?
The energy transferred per coulomb of charge
Where does a voltmeter go and why?
Parallel due to having a very high resistance
What is the equation for working out voltage?
V=W/Q
What is Kirchoff’s law for current in series?
That it is the same throughout
What is Kirchoff’s law for current in a parallel circuit?
The current into the junction = the current out if the junction
What is Kirchoff’s law for potential difference in series?
The sum of the P.d = The total E.M.F
What is Kirchoff’s law for potential difference in a parallel circuit?
The P.d is the same across each branch
What is Kirchoff’s law for resistance in a series circuit?
R1 + R2 = Rtotal
What is Kirchoff’s law for resistance in a parallel circuit?
1/R1 + 1/R2 = 1/Rtotal
What is resistivity?
The resistance of a 1m^2, 1m long sample of material
What is resistivity in relation to the material?
It is a property
What is the equation for resistivity?
R=PL/A
What is resistivity affected by?
- Cross sectional area
- Material
- Length
- Temperature
What is drift velocity?
The average speed particles travel along a conductor
What is the equation for drift velocity?
I = nAvq
I = current n = charge carrier density A = cross sectional area v = drift velocity q = charge
What is resistance?
The degree to which a component impedes the flow of current
How do you work out resistance?
R = V/I
How do you measure resistance?
Using a multimeter
What does a thermistor do?
A component thats resistance changes with temperature
What does an LDR do?
A light dependant resistor works as light increase the resistance of the component decreases
What is the equations for potential dividers?
L/L = Vout/Vsupply
What is a positive temperature coefficient and how do they work?
Resistance increases as temperature rises, due to lattice ions vibrating and more electron colliding with the ions
What is an Ntc and how does it work?
A negative temperature coefficient is where resistance goes down as temperature rises due to more conduction electrons being realised which allow for a higher current flow
What is E.M.F?
The energy gained per coulomb of charge passing through the supply
What is the internal resistance?
The resistance of the cell
What is the terminal P.d?
The P.d between the cell terminals
What are the lost volts?
The energy transferred per coulomb in moving through the cell
How do you work out E.M.F?
E.M.F = Terminal P.d + Lost Volts E = V + Ir
What is power?
Power is joules per second
How does a fixed resistor I-V graph look?
Line if Y=X due to having a fixed resistance making it an ohmic conductor
What does the I-V graph of a diode look like?
Flat line until a certain point on the X axis, due to a certain P.d needed for a change in current. Moreover current only flows in one direction
What does the I-V graph of a filament bulb look like?
Looks like an f passing through the origin, due to as current increase, temperature increases meaning that more electron collisions occur due to lattice vibrations. Moreover it is a non-ohmic conductor
