what is kirchoffs first law?

at any point in an electrical circuit the sum of currents into that point = sum of currents out of that point

what is the mean drift velocity

the average velocity of electrons moving through a wire

mean drift velocity equation

I=Anev I = current in conductor n = number density e = elementary charge v = mean drift velocity

what effect does a thinner wire have on the mean drift velocity

if current is constant then mean drift velocity has to increase as wire gets thinner

what does the ideal ammeter have

zero resistance

what is EMF

electro motive force

describes when work is done on charge carriers

where energy is transferred from other energy forms into electrical energy

what is PD

potential difference

describes when work is done charge carriers

when energy is transferred from electrical energy into other forms of energy

what is ohms law

for a metallic conductor kept at a constant temperature, the current in the wire is directly proportional to the potential difference across it

what is resistivity

an electrical property of a material.

resistance is proportional to length/area. the constant is resistivity

equation for resistivity

R= pl/A

as a material gets hotter what happens to its resistivity

as a material gets hotter, the resistivity increases

what are semiconductors

they have negative temperature coefficients so their resistance drops as thei temperature increases

what are thermistors made of

semiconductors

what is power

the rate of energy transfer

what is kirchoffs second law

the sum of electromotive forces is equal to the sum of pds around a closed loop

describe current in a series circuit

same in every position

describe voltage in a series circuit

emf is shared equally among resistors with the same resistance

if resistances are different then the resistor of higher resistance will take a higher proportion of the emf

total resistance in a series circuit

r1+ r2 +r3 e.t.c

describe current in a parallel circuit

current is shared between paths according to resistance. the higher the resistance the less current

describe voltage in a parallel circuit

pd across each branch is equal to emf in power supply

pd is shared between components in the branch

total resistance in a parallel circuit

1/R = 1/r1 + 1/r2 e.t.c

what is the difference between the pd in the circuit and the emf in the power supply

difference is lost volts

lost volts = Ir

I = current

r = internal resistance

how can you calculate emf

emf = terminal pd + lost volts

equation to find the force between two point charges

kQ1Q2/r^2 where k is a constant

other equation to find the force between two point charges

F=charge X electric field

IV graph for a diode

slopes up from around 0 one arm going up

IV graph for filament lamp

through origin, wavy arm going horizontal

equation for power

P=IV

equation for energy with voltage and current

E=VIt

what is EMF in terms of lost volts

emf=terminal pd + lost volts

equation for lost volts

lost volts = I X r where r= internal resistance