2.31 Electric Circuits

1. 2.31 Electric Circuits 10.3 Series and Parallel Circuits

2. Recap • Amps = rate of electrons flowing through a circuit • Can be measured using an ammeter that’s connected to a circuit in series • Volts (V) = how much energy the electrons are moving with (potential energy or difference in charge between the two ends) • measured by a voltmeter that has to be connected to the circuit in parallel to the load it is measuring

3. 2.4 – Series and Parallel Circuits • Circuits are described by the number of pathways that the electrons (current) are provided • Series circuits only have one pathway • Parallel circuits offer a choice of different pathways that an electron can flow through

4. 2.41 – Series Circuits and Current • When the light switch is off, the whole circuit is off • Because there is only one path for electrons to flow through, the current must flow through each load

5. 2.41 – Series Circuits and Current • Examples of series circuits: • Old Christmas light strands

6. 2.41 – Placement of Ammeter • Ammeters need to be connected to a circuit in series. A

7. 2.41 – Series Circuits and Current • The current is shared between all loads. • Therefore, Itotal = I1 = I2 = I3etc. I1 = 0.5 A I2 = 0.5 A I1 = 0.33 A I2 = 0.33 A I1 = 1.0 A I2 = 1.0 A I3 = 0.5 A I3 = 0.33 A Itotal = 1.0 A Itotal = 0.5 A Itotal = 0.33 A

8. 2.41 – Placement of Voltmeter • Voltmeters need to be connected to a circuit in parallel. • Remember: parallel circuits offer a choice of different pathways that an electron can flow through V

9. 2.41 – Series Circuits and Current • If more loads are added • each light will grow dimmer. This is because the potential of each load has been reduced. • The voltage of each load adds up to the voltage of the cell/battery • Vtotal = V1 + V2 + V3etc.

10. 2.41 – Series Circuits and Current • The voltage of each load adds up to the voltage of the cell/battery • Vtotal = V1 + V2 + V3etc. V1 = 9 V V1 = 4.5 V V2 = 4.5 V V1 = 3 V V2 = 3 V V3 = 3 V Vtotal = 9 V Vtotal = 9 V Vtotal = 9 V

11. 2.42 – Parallel Circuits and Current • Since electrons can choose which path to follow, when one switch is opened (turned off), the lights don’t all go off since there is more than one path for the current to follow.

12. 2.42 – Parallel Circuits and Current • The current is divided between each pathway • Comparable to the way water flows down a river and is divided between parallel channels • The current of each branch adds up to the total current. • Therefore, Itotal = I1 + I2 + I3etc

13. 2.42 – Parallel Circuits and Current • The current of each branch adds up to the total current. • Itotal = I1 + I2 + I3etc I1 = 0.6 I2 = 0.6 A A Itotal = 1.2 A

14. 2.42 – Parallel Circuits and Potential • All electrons leaving the battery have the same “incentive” or energy to bring them back into it, regardless of the path they take to get there. • Analogy: • Water flowing over the Canadian and American falls in Niagara Falls will travel from the same height and end up in the same place. Therefore, the energy is the same.

15. 2.42 – Parallel Circuits and Potential • Adding more paths doesn’t reduce the energy – or brightness of a bulb – it only draws more current – allows more electrons to travel through. • The voltage of each branch is the same as the voltage of the cell/battery • Vtotal = V1 = V2 = V3etc. V1 V2