1. Electrical Circuit (DC) analysis
Sections : pages ;

2. Potential difference (in a circuit)
Energy GAINED by electrons:
The electrons in a wire gain potential energy when passing through the cell or battery.
Electromotive force (emf) is the difference in the energy per unit charge (J·C-1, or Volts (V)) that the electrons have gained while passing through the cell or battery
NOT a force!
e.m.f is the work per unit charge made available (supplied) by an electrical source

3. Potential difference (in a circuit)
Energy USED by electrons
Potential Drop (difference): is the measure of the amount of energy per unit charge that has been used by an element within the circuit. (i.e. an electron uses energy to pass through a resistor; the amount of energy per unit charge (voltage) used is equivalent to the “Potential Drop” or “Voltage Drop” across that resistor.)
Resistors: energy transitions mainly to internal (thermal)
Lamps: energy transitions to radiant and internal/thermal

4. Electrical Power
Power: the rate at which work is done; the rate at which energy is transferred/used
𝑷= 𝑾 ∆𝒕
In a conductor with a potential difference, V, and a current, I, passing through it:
The amount of charge: 𝑰= 𝒒 ∆𝒕  ∆𝒕= 𝒒 𝑰
The energy transferred: 𝑽= 𝑾 𝒒  𝑾=𝑽𝒒
Power used in a circuit: 𝑃= 𝑊 ∆𝑡 = 𝑉𝑞 𝑞 𝐼 =𝐼𝑉
𝑷=𝑰𝑽

5. Major sources of e.m.f Electromagnetic
When a coil of wire is rotated in a magnetic field, an induced current is produced
Power stations use generators such as these to produce a current
Chemical
Oxidation-reduction reactions transfer electrons between chemicals
Dry cells, fuel cells, and batteries

6. Major sources of e.m.f Photoelectric effect
Electrons are emitted from certain metal surfaces when high frequency light is directed onto their surfaces
Photocells used in watches, clocks, automatic doors, etc.
Piezoelectric effect
Certain crystals can produce a charge on one side when placed under stress; a potential difference results
Used in Crystal microphones

7. Major sources of e.m.f Thermoelectric effect
When two pieces of certain metals are wound together and one end is heated while the other is cooled, a current is produced
Thermocouples—used in temperature-measuring devices (typically high-temperature measurements)

8. Review: What is necessary for a DC Circuit?
a Complete Circuit has:
A conducting pathway connecting two ends of …
A Source of Potential Difference,
Allowing current to flow through a…
Resistive Electrical Component that consumes electrical power
Note: DC = direct current current always flows in the same direction

9. Conventional Current vs. Electron Flow
Historically, the direction of the flow of charge carriers was defined to be from positive to negative
It is now known that current is a flow of electrons from negative to positive, however…
CONVENTIONAL CURRENT STILL IS DRAWN AND INTERPRETED AS FLOWING FROM POSITIVE TO NEGATIVE!

10. Conventional Current vs. Electron Flow

11. Post-Lab: Current and Voltage
How were the current and the voltage drop measured in last week’s lab?
Ammeter: a device used to measure the current flowing in a circuit or branch of a circuit
Always connected in series with the element for which the current is being measured
Ideal ammeter has zero resistance
Voltmeter: A device used to measure the potential drop across a circuit element
Always connected in parallel with the element for which the potential drop is being measured
Ideal voltmeter has extremely (infinitely) high resistance
Draw a circuit diagram for last week’s lab set-up

12. Post-Lab: Current and Voltage
What was the general relationship between the potential drop across your resistor and the current flowing through the resistor?

13. Ohm’s Law
“Provided the physical conditions, such as temperature, are kept constant, the resistance is constant over a wide range of applied potential differences, and therefore the potential difference [across the resistor] is directly proportional to the current flowing [through the resistor].”
𝑽=𝑰𝑹

14. Ohmic devices (ohmic conductors)
Those devices which obey the linear relationship of Ohm’s Law at all potential differences
Temperature of this device will NOT change due to the heating effect of the current as voltage changes
No device is truly completely Ohmic
Reserved for only an ideal resistor
Most devices would be considered Non-Ohmic

16. Non-Ohmic vs. Ohmic devices—Current vs. Voltage

21. Potential Dividers

22. Variable Resistors

23. Semiconducting Diodes

24. Thermistors

25. Circuit Analysis using Ohm’s Law