1. S.MORRIS 2006 ELECTRICAL CIRCUITS More free powerpoints at www.worldofteaching.com

2. The CELL The cell stores chemical energy and transfers it to electrical energy when a circuit is connected. When two or more cells are connected together we call this a Battery. The cells chemical energy is used up pushing a current round a circuit.

3. What is an electric current? An electric current is a flow of particles called electrons flowing through wires and components. + - In which direction does the current flow? from the Negative terminal to the Positive terminal of a cell.

4. simple circuits Here is a simple electric circuit. It has a cell, a lamp and a switch. To make the circuit, these components are connected together with metal connecting wires. Wires are conductors since they conduct electricity. cell lamp switch wires

5. simple circuits When the switch is closed, the lamp lights up. This is because there is a continuous path of metal for the electric current to flow around. If there were any breaks in the circuit, the current could not flow.

6. circuit diagram cellswitchlampwires Scientists usually draw electric circuits using symbols;

7. circuit diagrams In circuit diagrams components are represented by the following symbols; cellbatteryswitchlamp motorammetervoltmeter buzzer resistorvariable resistor

8. types of circuit There are two types of electrical circuits; SERIES CIRCUITSPARALLEL CIRCUITS

9. The components are connected end-to-end, one after the other. They make a simple loop for the current to flow round. SERIES CIRCUITS If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.

10. PARALLEL CIRCUITS The current has a choice of routes. The components are connected side by side. If one bulb ‘blows’ there is still be a complete circuit to the other bulb so it stays alight.

11. Opened and Closed Circuits If a switch in a circuit is closed and allows for the flow of electricity, it’s called a “closed circuit” If you open the switch and stops the flow of electricity, it’s called an “open circuit”

12. measuring current Electric current is measured in amps (A) using an ammeter connected in series in the circuit. A

13. measuring current A A This is how we draw an ammeter in a circuit. SERIES CIRCUIT PARALLEL CIRCUIT

14. measuring current SERIES CIRCUIT PARALLEL CIRCUIT current is the same at all points in the circuit. 2A current is shared between the components 2A 1A

15. copy the following circuits and fill in the missing ammeter readings. ? ? 4A 3A? ? 1A ? 3A 1A

16. measuring voltage The ‘electrical push’ which the cell gives to the current is called the voltage. It is measured in volts (V) on a voltmeter V

17. Different cells produce different voltages. The bigger the voltage supplied by the cell, the bigger the current. measuring voltage Unlike an ammeter a voltmeter is connected across the components Scientist usually use the term Potential Difference (pd) when they talk about voltage.

18. measuring voltage V This is how we draw a voltmeter in a circuit. SERIES CIRCUITPARALLEL CIRCUIT V

19. V measuring voltage V V V

20. series circuit 1.5V voltage is shared between the components 1.5V 3V

21. voltage is the same in all parts of the circuit. 3V parallel circuit 3V

22. measuring current & voltage copy the following circuits on the next two slides. complete the missing current and voltage readings. remember the rules for current and voltage in series and parallel circuits.

23. measuring current & voltage V V 6V 4A A A a)

24. measuring current & voltage V V 6V 4A A A A b)

25. answers 3V 6V 4A 6V 4A 2A 4A a)b)

26. Resistors Resistors “resist” the flow of electrons in the circuit. Electrons strike a lot of particles and emit as heat. When electronics get warm, it’s the resistance in the circuit heating up. Without them, the current would flow uncontrolled and short the circuit. As resistance gets bigger, current gets smaller. You can control current this way. Symbol

27. Measuring Resistance The unit for a resistor is called an ohm For example: A wire with 1 ohm of resistance powered by 1V of pressure, will push 1 amp of current through the circuit. Ohmmeters are used to measure resistance Galvanometers measures very small currents 1 V 1 ohm 1 Amp

28. Ohm’s Law Georg Ohm discovered the relationship between voltage, current, and resistance As resistance goes up, current goes ____ As voltage goes up, current goes ___ As resistance goes down, current goes __ As voltage goes down, current goes ____ Down Up

29. Calculating Resistance If a car battery at 12V supplying 1 amp of current into a car light, what is the resistance of the light? V=IxR ___ 12 V = 1 A 12 ohms

30. Calculating Current If you stack two D-cell batteries together, you get (1.5V+1.5V = 3V). How much current is going to flow through a 10 ohm wire? V=IxR ___ 3 V = 10 ohms 0.3 Amps

31. Power Power (heat) in circuits is measured in Watts. Power = Voltage x Current P = V x I For example, 100V x 1 Amp = 100 Watts What’s the current of a 100W light bulb? P=VxI 100W/120V = 0.83 ohms

32. Energy Energy is Watts over time Energy = Power (kW) x Time (hours) E = P x T For example, a 1000W hair dryer running for 1 hour uses 1 kilowatt hour. How many kWh will 10 100W light bulbs burn in 30 minutes? 100W * 10 bulbs = 1000W E = 1kW * 0.5 hours E = 0.5kW hours Turn off those lights!