1. Chapter 17 Current electricity

2. Conventional Current and Electron Flow

3. 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

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

5. 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

6. 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

7. 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

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

9. 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.

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

11. Resistance
May be fixed or variable
Variable resistor (rheostat)

12. Resistance

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

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