Electric Circuit

Name	Definition	Formulae
ELECTRICITY
Electron-volt	Energy transferred when an electron moves through a potential difference of one volt	$1ev=1.6times 10^{-19}J$
Motion of electron in a wire	Drift velocities	$V_{random}=10^{6}m/s$ $V_{drift}=10^{-4}mm/s$
Current	The rate of flow of charged particle n: charge carrier number density Different metals have different conductivity because different n	$I=frac{Delta Q}{Delta t}$ $I=nev_{drift}A$
Potential difference	The energy/charge transferred between two point	$V=frac{W}{Q}$
emf	WD per unit charge to move a charge around the circuit Emf = pd when I = 0 because no energy / pd lost on resistors	$V=frac{W}{Q}$
	Plot V (across battery) against I Gradient = -r Y intercept is emf
Resistance	The opposition to the flow of electrical current	$R=frac{V}{I}$
Ohm’s Law	A special case where for constant temperature
Total resistance	$R_{TOTAL}=R_{1}+R_{2}.....R_{n}$ $R_{2} frac{1}{R_{TOTAL}}=frac{1}{R_{1}}+frac{1}{R_{2}}...frac{1}{R_{n}}$
Resistivity	Numerically equal to the resistant of a unit length a unit area of wire	$R=frac{pl}{A}$
Power	$P=IV=I^{2}R=frac{V^{2}}{R}$
Critical temperature	The temperature below which its resistivity instantly drop to zero

Current-potential Graph
Ohmic conductors	Filament bulb	Diodes	Thermistor	LDR



Obeying Ohm’s Law	↑ current flow, Temperature ↑ Ions vibrates more, probability of collision ↑, electron lose more energy ↓ so resistance ↑	Forward direction: low R Require a minimum driving V in the forward direction Threshold voltage 0.6V Backward direction: high R Few charge carriers → leakage Reverse pd high enough overcome E barrier	Temperature ↑, more energy transfer to lattice ions Electrons to conduction band charge carriers density ↑,current↑ resistance ↓	Electrons gain energy from light Light intensity ↑, electrons to conduction band Charge carriers density ↑, current ↑ resistance ↓