1. ELECTRICAL CIRCUITS
All you need to be an inventor is a good imagination and a pile of junk.
-Thomas Edison
Lesson Objectives:
To explain the difference between current, voltage and resistance in an electrical circuit.
To demonstrate that you can measure current, voltage and resistance in an electrical circuit.

2. How you should be thinking about electric circuits:
Voltage: a force that pushes the current through the circuit (in this picture it would be equivalent to gravity)

3. How you should be thinking about electric circuits:
Resistance: friction that impedes flow of current through the circuit (rocks in the river)

4. How you should be thinking about electric circuits:
Current: the actual “substance” that is flowing through the wires of the circuit (electrons!)

5. I = V / R Ohm’s Law I = Current (Amperes) (amps) V = Voltage (Volts)
R = Resistance (ohms)
Georg Simon Ohm ( )

6. Would This Work?
Teacher Notes: No. Incomplete circuit.

7. Would This Work?
Teacher notes: No, the circuit is going from positive to positive. It must flow from positive to negative.

8. Would This Work?
Teacher notes: Yes!

9. The Central Concept = Complete Circuit

10. circuit diagram
Scientists and engineers draw electric circuits using symbols;
cell
lamp
switch
wires

11. Series and parallel Circuits
Series circuit
All in a row
1 path for electricity
1 light goes out and the circuit is broken
Parallel circuit
Many paths for electricity
1 light goes out and the others stay on

12. 3 2
Teachers Note: The current decreases because the resistance increases (Ohms Law says that I = V/R). The voltage in the system is constant. 1
The current decreases because the resistance increases. Ohm’s Law
says that I=V/R. The voltage in the system is constant, resistance increases.

13. PARALLEL CIRCUIT
Place two bulbs in parallel. What do you notice about the brightness of the bulbs?
Add a third light bulb in the circuit. What do you notice about the brightness of the bulbs?
Remove the middle bulb from the circuit. What happened?

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

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

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

17. Fill in the missing ammeter readings...? 3A 3A 4A ? 1A ? ? 4A 4A 1A ? 1A

18. 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

19. measuring voltage
Different cells produce different voltages. The bigger the voltage supplied by the cell, the bigger the current.
Scientist usually use the term Potential Difference (pd) when they talk about voltage.

20. measuring voltage V V This is how we draw a voltmeter in a circuit.
SERIES CIRCUIT
PARALLEL CIRCUIT

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

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

23. OHM’s LAW Voltage Current Resistance Parallel Circuit Voltage Current
Measure the current and voltage across each circuit.
Use Ohm’s Law to compute resistance
Series Circuit
Voltage
Current
Resistance
Parallel Circuit
Voltage
Current
Resistance

24. 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.

25. measuring current & voltage

26. measuring current & voltageb) 6V 4A A V A V A

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