1. What are electric circuits?
There is a pump that pushes water around the system.
The water everywhere starts to move at the same time.
There are pipes that carry the water.
The water flows through the pipes.

2. Electric Circuits

3. Electric Current
The orderly flow of negative charges carried by electrons.
Conventional current direction is the direction a positive particle would flow: from positive to negative.
However, electrons flow from negative to positive.

4. Current

5. Electric Current (Current Intensity)
Current intensity is a measure of how many electric charges (e-) flow past a specific location in the circuit, in one second.
The symbol is I.
The SI unit is ‘ampere’ (A).
I = Current (A)
Q = Charge in Coulombs (C)
∆ t = Time elapsed (seconds)

6. Amount of charge (Q) measured in coulombs (C)
Current intensity (I) measured in amperes (A)
Time (t) measured in seconds (s)

7. Example: What is the current intensity if 10 C of electric charge is measured in 5.0 seconds?
Q = 10C
∆ t = 5.0 s

8. 2. a) Determine the amount of electric charge when 0
2. a) Determine the amount of electric charge when A of current is measured in 4 seconds.
I = 0.2A ?
Q = ?
∆ t = 4 s
b) How many electrons would this represent?

10. Measuring Current Current intensity is measured using an ammeter.
An ammeter must be connect in series (beside) the load (e.g. light bulb or resistor) through which you wish to measure current intensity.
Connect the ammeter’s –ve terminal to the –ve terminal of the power supply (and +ve to +ve).

11. Notice the symbols! More to come…
Battery
Ammeter
Wires are always drawn with straight lines.
Light bulb
Notice the symbols! More to come…

13. Potential Difference/Voltage
Electrical potential is the energy transferred between two points in an electrical circuit.
This energy is carried by the charges: when flowing from one point to another, the charges transfer their energy to other components.
This energy is supplied by the battery or power source.
We measure this potential difference between two points in a circuit.

14. D C
Charges carry energy, provided by the power source (ex: battery).
Energy is used to operate a device (ex: light bulb).
Voltage (or potential difference) is measured across two points:
Between A and B: difference of 2 V
(energy is given to light bulb)
Between C and D: difference of 2 V
(energy, from the battery, is ‘restored’ to flowing charges) A B

15. Voltage
Potential difference is a measure of how much energy is carried per coulomb and transferred between two points in a circuit.
SI symbol is V
SI unit is the ‘volt’ (V)
V = potential difference in volts (V)
E = energy transferred in joules (J)
Q = charge in coulombs (C)

16. Example
A wide variety of batteries are available on the market. What is the energy supplied by a 1.50V battery if 200C of charge flow through an electrical appliance?

17. Measuring Voltage
Potential difference (voltage) is measured using a voltmeter.
A voltmeter must be connected in parallel  around the load through which you wish to measure potential difference.
Always connect the voltmeters –ve terminal to the –ve terminal of the power supply (and +ve to +ve).

18. Voltmeter

19. Current and Voltage