Current electricity The basics Definitions, working and measurements

R A V Simple circuit Electric current: flow of charges (electrons: e - ) e - Atoms in copper wire have loose valence e - : sea of delocalised electrons Enlarged piece of wire e - When battery connected: e - flows in one direction (- to +) e - e - e - e - Measures current strength ( I ) Rate of flow of charge (Q) I = Q ΔtΔt Connected in series (just counting charges in certain time) Low resistance (charges are to flow easily) Measures (electrical) potential (energy) difference in volts (V) Thus energy per charge transferred between two points V = W Q Connected in parallel High resistance (take HIGH reading of energy and LOW reading of energy and subtract to give difference). No current flows through! HIGH energy LOW energy (Q = I t) (1V=1J  C -1 ) (1A=1C  s -1 ) Measures potential difference (pd) in volts (V) If 5e - flow into R, 5 e - come out the other side (they have less energy)

R A V Simple circuit Electric current: flow of charges (electrons: e - ) e-e- Atoms in copper wire have loose valence e - : sea of delocalised electrons Enlarged piece of wire e-e- When battery connected: e - flows in one direction (- to +) e-e- e-e- e-e- e-e- Measures current strength ( I ) Rate of flow of charge (Q) I = Q ΔtΔt Connected in series (just counting charges in certain time) Low resistance (charges are to flow easily) Measures potential difference (pd) in volts (V) Thus energy per charge transferred between two points V = W Q Connected in parallel High resistance (take HIGH reading of energy and LOW reading of energy and subtract to give difference). No current flows through! HIGH energy LOW energy (Q = I t) (1V=1J  C -1 ) (1A=1C  s -1 ) If 5e - flow into R, 5 e - come out the other side (they just have less energy)

Ohm’s Law The relationship between pd and I is established There is a ……….. ………….. between potential difference and current strength at constant temperature

Ohm’s Law The relationship between pd and I is investigated. Set up a table to take readings R V A

Ohm’s law Current strenght controlled by number of cells or a reostat (variable resistor)

Ohm’s Law cnt. Ohm’s law: There is a ……….. …………………. between potential difference and current strength at constant temperature (ohmic relationship) direct proportionality If temperature not constant – non-ohmic relationship (not straight line) R V A

Non-Ohmic Conductors (or resistors) not adhering to Ohm’s law are non-ohmic conductors