Chapter 17 Current electricity

Conventional Current and Electron Flow

Conventional Current and Electron Flow Electric current (I) is rate of flow of charges I = Q ÷ t Q = It Charge = current × time SI unit for electric current is ampere (A) or coulomb per second (C s−1) 1 A = _____ C s−1

Measuring electric current Ammeter used to measure size of an electric current Must be connected in series to circuit

Electromotive Force The electromotive force (e.m.f.) is the work done by the source in driving one coulomb of charge around a complete circuit SI unit is volt (V) or joules per coulomb (J C−1) 1 V is equivalent to 1 J C−1

Potential Difference Potential difference across a component in a circuit is the work done to drive one coulomb of charge through the component SI unit is volt (V) or joules per coulomb (J C−1) Formula to calculate e.m.f or p.d: V = W ÷ Q W = Q x V Potential difference = work done ÷ charge

Potential Difference Potential Differences around a Simple Circuit The sum of all e.m.f.’s must be equal to the sum of potential difference across all the components in the circuit E1 + E2 = V1 + V2 + V3

Potential Difference Measuring Potential Difference A voltmeter can measure potential difference across two points Must be connected in parallel to the component

Resistance Resistance is the ratio of the potential difference across the object to the current flowing through it Resistance = Potential difference ÷ current R = V ÷ I SI Unit is ohm () When R increases, _______ increases.

Resistance Resistors A component in an electrical circuit which provides a known value of resistance

Resistance May be fixed or variable Variable resistor (rheostat)

Resistance

Resistance Resistors in Series R = R1 + R2 + R3 Effective resistance is sum of individual resistances

Resistance Resistors in Parallel Reciprocal of effective resistance is sum of reciprocals of individual resistances