1. Circuits and Circuit Elements
Electricity
Circuits and Circuit Elements

2. Circuits
Electric circuit – a set of electrical components connected so that they provide one or more complete paths for the movement of charges
Charges move from the battery through a path back to the battery

3. Circuits Switches are used to open and close the circuit
If the circuit is open, there is no complete path for the charge to travel
If the circuit is closed, there is at least one complete path for the charge to travel
Charge cannot flow, so there is no current

4. Circuits
Schematic diagram – a graphic representation of an electric circuit or apparatus, with standardized symbols for the circuit components

5. Circuits

6. Series and Parallel Circuits
Series – describes a circuit or portion of a circuit that provides a single conducting path
One path for current to travel
If one element is removed, the circuit will not work
If one element doesn’t work, the circuit will not work

7. Series and Parallel Circuits
Parallel – describes components in a circuit that are connected across common points, providing two or more separate conducting paths
More than one pathway
Charge moves through the path of least resistance
If one part is removed or doesn’t work the circuit may continue to work

8. Electric Power and Electrical Energy
Electrical energy – the energy associated with electrical charges, whether moving or at rest
Electric power – the rate at which electrical energy is used in a circuit
The rate at which electrical work is done
Power = Current * Potential Difference
P=IV
Power = (Current)2 * Resistance
P=I2R
Power = (Potential Difference)2 / Resistance
P= V2 / R
Measured in Watts (W)
Electric companies measure energy consumed in kilowatt-hours (kWh)
The greater the power produced by a given current or potential difference, the smaller the resistance

9. Fuses and Circuit Breakers
Overloaded – condition when electrical wires carry more than a safe level of current
Short circuit – accidental creation of an alternative pathway
Reduces the resistance in the circuit
Increases the current

10. Fuses and Circuit Breakers
Short circuits
Leads to overload
Grounding is used to prevent electric shock from short circuits
Fuse – an electrical device containing a metal strip that melts when current in the circuit becomes to great
Used to prevent overload

11. Fuses and Circuit Breakers
Circuit breaker – a device that protects a circuit from current overloads
Trip when the current overloads
Acts like a switch

12. Resistors in Series
Series – describes a circuit or portion of a circuit that provides a single conducting path without junctions
When resistors are arranged in series, the current flowing through each resistor is the same
Equivalent resistance – the total resistance of a circuit

13. Resistors in Series

14. Resistors in Series
For resistors in series, the equivalent resistance is equal to the sum of all of the resistors
Req = R1 + R2 + R3…
Total Potential difference (voltage) = Current * Equivalent Resistance
VTot = IReq
The equivalent resistance of a series combination of resistors is always greater than any individual resistance

15. Resistors in Series
Potential difference across a given resistor can be calculated by multpying the current (which is constant) by the resistance of the given resistor
V1 = IR1 or V2 = IR2
In a series circuit, all of the elements must be able to conduct electrical charge
If one bulb goes out or one wire gets disconnected, the entire circuit fails

16. Resistors in Parallel
Parallel – describes two or more components in a circuit that are connected across common points or junctions, providing separate conducting pats for the current
There is more than one pathway through the circuit or part of a circuit
Resistors in parallel have the same potential difference across them
V is constant
The sum of the individual currents in parallel resistors equals the total current
ITot = I1 + I2 + I3 …

17. Resistors in Parallel

18. Resistors in Parallel
The equivalent resistance of resistors in parallel can be calculated using a reciprocal relationship
1/Req = 1/R1 + 1/R2 + 1/R3 …
The equivalent resistance is always less than the smallest resistance in the group of resistors
Parallel circuits do not require all elements to conduct
The circuit will continue so long as there is at least one complete pathway from one terminal to the other

19. Resistors in Parallel

20. Resistors Combined Both in Parallel and in Series
Complex circuits have resistors arranged both in series and in parallel
You must simplify the groups of resistors
Work with a small group that is all in series or in parallel
After you have simplified the small groups, start combining groups until you have “created” a de facto simple circuit
Work backward to find current or potential difference

21. Resistors Combined Both in Parallel and in Series

22. Resistors Combined Both in Parallel and in Series