IB Physics 2 Electric Circuits

Current (definition)

the rate of flow of electric charge

What is the cause of resistance in a wire

Collisions between conduction electrons and lattice ions

Ohms law

For a conductor at a constant temperature, the current through it is proportional to the potential difference across it over a wide range of potential differences

What properties of a wire make it a good conductor

short, fat, cold

V (electric potential) = (formulas and units)

Ep/q, W/q, V, J/C

E (electric field) = (formulas and units)

F/q, V/d, kQ/r², N/C, V/m

W (work) = (formula and units)

qV, Ep, J, eV (electronvolt), kWh

Work, energy = (formulas)

E=W=Q=Pt=VIt=I²Rt=V²t/R

Current = (formula and units

V/R, (change in q)/t, A, C/s

v (speed) formula

I=nAvq, n=number charge carriers per unit volume

R (resistance)= (formula and units)

V/I, pL/A (p=resistivity in ohm x meters), ohms

P (power) = (formula and units)

VI=I²R=V²/R, W

1 eV = 1 elementary charge =

1.60 × 10^-19 J

1 kWh =

3.6 × 10^6 J

In series:

Current…

Voltage…

Resistance…

Power…

(current) Same for all resistors, It=I1=I2

(voltage) Splits in proportion Vt=V1+V2…

(resistance) adds up Rt=R1+R2…

(power) adds up Pt=P1+P2…

In parallel:

Current…

Voltage…

Resistance…

Power…

(current) Splits in proportion It=I1+I2…

(voltage) Same for all resistors, Vt=V1=V2

(resistance) adds down 1/Rt=1/R1+1/R2…

(power) adds up Pt=P1+P2…

electromotive force=

emf, total energy per unit charge supplied around a circuit by the battery

Terminal potential difference

the energy per unit charge available for use by only the external circuit

emf can be measured by

measuring the terminal pd of the cell when no current is following

ε/emf (epsilon = ε) = (formula)

I(R+r) where R= external resistance and r=internal resistance

diode

a semiconductor device that allows current to flow in one direction only

Light dependent resistor (LDR): as intensity of light on the sensor increases, its resistance…

decreases

Thermistor (thermal resistor): as the temp of the thermistor increases, its resistance…

decreases

Variable resistor

a resistor whose resistance can be changed

Potentiometer

a variable resistor with a slider that acts as a potential divider

when measuring IV characteristics of a filament lamp, a potentiometer is placed…

in parallel with the lamp to get the full range of IV values