2. © JOHN PARKINSON 1

3. © JOHN PARKINSON 2

4. © JOHN PARKINSON 3 E L E C T R I C C U R R E N T Electrons Positive Ions Negative Ions Positive Holes

5. © JOHN PARKINSON 4 + Current (positive charge) flows from POSITIVE to NEGATIVE +++++++ Charge Q is measured in Coulombs [ symbol C ] Current I is measured in Amps [ symbol A]A] CURRENT = RATE OF FLOW OF CHARGE +ve-ve

6. © JOHN PARKINSON 5 + - II Conventional flow of Current in a Circuit

7. © JOHN PARKINSON 6 e-e- +ve-ve Electrons flow from NEGATIVE to POSITIVE Conventional Current - I

8. © JOHN PARKINSON 7 CURRENT = THE CHARGE FLOWING +++ PER SECOND AMPS = COULOMBS per SECOND AMPS = COULOMBS per SECOND

9. © JOHN PARKINSON 8 1.A Conducting Path 2.A Source of Potential Difference – p.d. i.e. a source of VOLTS - V A source of volts is referred to as an e.m.f. …… an Electro Motive Force source e.g. Cell [battery], Generator or Thermocouple COLDCOLD COLDCOLD coldhot V

10. © JOHN PARKINSON 9 RELATIONSHIP BETWEEN I and V Applying a Potential Difference between two points on a conductor produces a current Over a limited range of V, the current is sometimes proportional to the voltage. V = I R R is the Resistance in the circuit In Ohms (Ω)

11. © JOHN PARKINSON 10 Resistance can be thought of as a proportionality constant between I and V if Ohm’s Law applies. It is also the opposition to the flow of current. V = I R OHM’s LAW “The current through an ohmic conductor is directly proportional to the potential difference across it, provided there is no change in physical conditions e.g. temperature.” V I R

12. © JOHN PARKINSON 11 Ohmic and non-ohmic conductors V -V -I I Ohmic eg resistor or a piece of wire Gradient

13. © JOHN PARKINSON 12 Ohmic and non-ohmic conductors V -V -I I Non-ohmic eg diode forward bias reverse bias switch on pd for silicon = 0.6V

14. © JOHN PARKINSON 13 Ohmic and non-ohmic conductors V -V -I I Non-ohmic eg filament bulb

15. © JOHN PARKINSON 14 RESISTORS Colour codes are used to identify resistance value Circuit symbol R The Resistor Colour Code ColourNumber Black0 Brown1 Red2 Orange3 Yellow4 Green5 Blue6 Violet7 Grey8 White9 The four colour code bands are at one end of the component. Counting from the end, the first three (or sometimes four or five) bands give the resistance value and the last the tolerance TOLERANCES BROWN1% RED2% GOLD5% SILVER10% NONE20%

16. © JOHN PARKINSON 15 AA B A = ? B = ? 47 OOO , 1% Tolerance 47 OOO , 1% Tolerance

17. © JOHN PARKINSON 16 Resistivity (  )  depends on the type of material and temperature Units of  ohm m (  m) R  How does resistance depend upon length? How does resistance depend upon cross sectional area? R  1/A A A

18. © JOHN PARKINSON 17 Temperature / 0 C Resistance /  Variation of Resistance [resistivity] with temperature semiconductor insulator metal Metal – more ion vibration impedes electrons Semiconductor – more ion vibration outweighed by more charge carriers Insulator – thermal energy releases more charge carriers

19. © JOHN PARKINSON 18 Power, Voltage and Current The Current Current indicates how many Coulombs Coulombs flow each Second The Voltage Voltage indicates how much energy each coulomb carries The energy carried per second is the POWER The power (in joules per second) = coulombs per second x joules per coulomb Current (I)Voltage (V) A joule per second is called a watt ( W ) The Energy Energy carried is measured in Joules So work done W = Q V ( = I t V ) Joules P = I V

20. © JOHN PARKINSON 19 PLUGS AND FUSES 3 A13 A Light Sound Heat Motion 5 A up to 720W 720-3000W live neutral earth