electricity Flashcards
define current
the change in charge per second/ rate of change of charge
give the formula for current using charge
I = change in Q/ change in t
define voltage
the work done in moving 1 coulomb of charge
give the formula for voltage using work done
V = W/Q
what is ohm’s law formula
V = IR
what is represented by the gradient on an IV graph
the resistance
what is the formula for Rt in series
R1 + R2…
what is the formula for Rt in parallel
1/R1 + 1/R2 = 1/Rt
what does adding resistors in a parallel circuit do?
decrease the total resistance
if 2 resistors are in parallel and are of the same value of R, what is Rt
half R
experimental description for the IV curve of a bulb
the graph is a cubic curve and therefore resistance isn’t the gradient anymore, at any point the gradient is just voltage/current at that point. as the voltage increases, the current will also increase, there will then be an increase in the temperature of the filament due to an increase in the number of collisions between electrons and filament ions, which in turn will increase the total resistance.
reverse bias diode explanation
- diodes only allow current flow one way
- reverse bias is when a diode is facing the opposite way and thus you get negative voltages
- there will be no current flow with a very low current value
- resistance will be very high
diode breakdown
reverse bias above the breakdown value (usually about 50V), this will cause there to be a large current and a 0 resistance.
forward bias diode explanation
A positive voltage above the threshold voltage (around 0.6V) will cause a large current flow with very low resistance.
However, a positive voltage below the threshold will cause no current flow with large resistance.
what is the formula for resistivity
rho = RA/L
what does A represent in the formula for resistivity?
Cross-Sectional Area
How do you calculate the CSA of a wire?
pi x radius^2 / 4
the gradient of a resistivity graph is what?
rho/A
Bullet point the experimental description for resistivity
- record the diameter for the wire using a micrometer in 3 places along the wire to calculate an average.
- measure the length of the wire using a ruler
- measure the resistance of the wire using an ohmmeter
- repeat the readings for 7 lengths of wire
- plot a resistance/length graph
- take the gradient
- calculate the CSA
- use resistivity = gradient x CSA
what happens when more light falls upon an LDR
the resistance will decrease
what happens as the temperature of a thermistor increases
the resistance will decrease
ammeters have
very low voltage
voltmeters have
infinite reistance
potential dividers for 1 resistor equation is
V/Vt = R/Rt
potential dividers equation across a resistor is
Vout/Vin = Rout/Rt
what is EMF
electromotive force
EMF formula (1) is
EMF = E/Q
EMF formula (2) is
EMF = I(R+r)
EMF lost volts formula
EMF = Circuit resistace + lost volts(Ir)
define power
power is the energy transferred in 1s or the rate of change of energy.
Unusual power formula
P =E/t
what happens when the temperature of a superconductor drops
the resistance will drop until it eventually drops to 0.
where do superconductors drop to 0 resistance
below the critical temperature of that superconductor
