2. P5 Electric Circuits

3. Electric charge – objects become charged when electrons are transferred to or from them, for example, by rubbing Two types of charge are positive and negative (these names are just labels) Two objects with the same charge repel each other Two objects with different charges attract each other

4. + metal ions electrons The electrons experience resistance when they flow through the metal. The potential difference (voltage) provides energy which makes the electrons move through the metal ie it generates a current. potential difference The symbol for voltage is V The symbol for current is I The symbol for resistance is R Metal wire Normally the free electrons in a metal move around slowly at random. current  voltage resistance

5. V v1v1 v2v2 I i1i1 i2i2 I = i 1 = i 2 The current is the same everywhere V = v 1 + v 2 SERIES The sum of the voltages across each component equals the supply voltage R= r1r1 + r2r2 Resistance

6. I i1i1 i2i2 PARALLEL Current I3I3 i4i4 i5i5 I = I 3 I 1 = I 4 I 2 = I 5 I = I 1 + I 2 Current does not get used up Total current = the sum of the currents through each component

7. V v1v1 v2v2 V = v 1 = v 2 The voltage across each component is the same as the supply voltage. PARALLEL Voltage = energy per unit of charge

8. If more bulbs are added in parallel to a circuit then they will all be as bright as normal and more current is drawn from the power supply The potential difference is largest across the component with the greatest resistance, because more energy is transferred by the charge flowing through a large resistance than through a small one The current is smallest through the component with the largest resistance, because the same battery voltage causes more current through a smaller resistance than a bigger one

9. 12 V 4 V5 V 2A i3i3 SERIES v3v3 1 ohm3 ohmr3r3 i 3 = 2 Av 3 = 3 Vr 3 = 2 ohm

10. 12 V v2v2 PARALLEL 1 A i3i3 4 A r3r3 i 3 = 2 A v 2 = 12 V 12 ohm

11. Current is a flow of electrons Electrons have charge (negative) So current is a flow of charge How do we quantify current ? Current is the amount of charge flowing in a particular amount of time

12. Voltage provides energy to the electrons Electrons have charge (negative) So Voltage provides energy to the charge How do we quantify voltage ? Voltage is the amount of energy a particular amount of charge has

13. What about resistance ? All components will offer resistance to a flow of electrons How do we quantify resistance ? If a current of 1A flows through a component when the voltage across it is 1V then the component is said to have a resistance of 1 ohm [ 1 

14. I V R = Multiply both sides by R I V R = R xx R R I = VOr V = I R TakeV = I Rand divide both sides by I V I R II = V I =R or V I =R

15. I V R = V = I R V I =R V IR Q. A current of 4 A flows through a circuit with resistance 3 WW hat is the voltage ? use V = I R V = 4 x 3Voltage = 12 current = voltage / resistancevoltage = current x resistanceresistance = voltage / current V

16. Q. A current of 5 A flows through a circuit with voltage 10 V WW hat is the resistance ? V IR V I =R use R = 10 5 resistance = 2 Q. A circuit with voltage of 6 V h h as a resistance of 2 . What current should flow ? use V R =II = 6 2 current = 3  A

17. Q. A current of 4 A flows through a circuit with voltage 12 V WW hat is the resistance ? V IR V I =R use R = 12 4 resistance = 3 Q. A circuit with voltage of 8 V h h as a resistance of 2 . What current should flow ? use V R =II = 8 2 current = 4  A Q. A current of 60 A flows through a circuit with resistance 4 WW hat is the voltage ? use V = I R V = 60 x 4Voltage = 240V I V R = V = I R V I =R

18. Q. A current of 2 A flows through a circuit with voltage 16 V WW hat is the resistance ? V IR V I =R use R = 16 2 resistance = 8 Q. A circuit with voltage of 230 V h h as a resistance of 5 . What current should flow ? use V R =II = 230 5 current = 46  A Q. A current of 25 A flows through a circuit with resistance 3 WW hat is the voltage ? use V = I R V = 25 x 3Voltage = 75V I V R = V = I R V I =R

19. The higher the temperature the lower the resistance The greater the light intensity the lower the resistance

20. Variable resistors Resistors are used in circuits to control the size of the current Two resistors in series have a larger resistance than one on its own. Connecting two resistors in parallel makes a smaller total resistance Two resistors in series make a potential divider

21. Voltage (V) Current (A) Current through a filament bulb Current is less here due to the extra resistance of the heating effect

22. Power = current X voltage (watt,W) (ampere, A) (volt, V) If you know the power, it is easy to calculate how much work is done (or how much energy is transferred) in a given period of time: Work done (or energy transferred) = power x time (joule, J) (watt, W) (second, s)

23. AC generator DC generator The size of the induced voltage can be increased by: increasing the speed of rotation of the magnet or electromagnet or coil; increasing the strength of its magnetic field; increasing the number of turns on the coil; placing an iron core inside the coil Generators produce a voltage by a process called electromagnetic induction AC = alternating current

24. If a magnet is moving out of the coil, or the other pole of the magnet is moving into it, there is a voltage induced in the opposite direction

26. Vp / Vs = Np / Ns Voltage across primary coil Voltage across secondary coil Number of turns primary coil Number of turns secondary coil = 8 turns4 turns Transformer

27. Rate/speed of rotation Strength of magnet/ magnetic field Number of turns/coils of wire

28. a.c / alternating current

29. Energy = power x time Power = energy / time

30. £0.78 2990

31. 30 ohm