1. CHAPTER TWO CONTINUED

2. VOLTAGE Electrical pressure or potential The Electromotive force that causes the movement of electons Electrical pressure is measured in volts Automotive electrical systems run on 12 volts

3. CURRENT Is the rate of electron flow Measure in amperes or amps As voltage goes up, current goes up As voltage goes down, current goes down

4. RESISTANCE Opposition to current flow – measured in ohms Size, type, length, temperature and physical condition of conductor affect its resistance An increase in resistance causes a decrease in current flow. Voltage drops as current flows through resistance

5. VOLTAGE DROP Is the amount of electrical pressure lost or consumed as it pushes current through a resistance The Sum (total) of all voltage drops in an electrical circuit will always equal source voltage – all the voltage is used up.

6. OHMS LAW E = Voltage I = Current flow R = Resistance E / I = R E / R = I I x R = E

7. TRY THESE… E=12V R=12  E=? R=120  E=12V R=24  E=12V R=? I=24A 

8. CAPACITANCE Stores electrical charges Does not consume any voltage Absorbs voltage changes – Spikes Discharges back into circuit Rated in farads and microfarads

9. ELECTRICAL CIRCUITS A simple automotive circuit has three parts: –Battery (power source) –Wires (conductor) –Load (lights motors) A circuit must have continuity, protective devices (fuses), and controls (switches)

10. SERIES CIRCUIT Only one path for current to flow Total resistance is the sum of all resistances Current flow through each resistor is the same Current flow is the same throughout the circuit Voltage drop across each resistor will vary if the reistor values are different The sum of all voltage drops will equal source voltage

11. PARALLEL CIRCUIT Two or more paths for current to flow Voltage applied to each leg is the same Voltage dropped across each leg will be the same –If more that one resistor in a leg, voltage drop will depend on the resistance of each resistor in that leg Total resistance will always be less than the resistance of any of its legs Current flow through the legs will differ if resistance is different The sum of the current in each leg equals the total current in the parallel circuit

12. SERIES-PARALLEL CIRCUITS Is a combination of series and parallel circuits

13. DIGITAL VOLT OHM METER – DVOM Values are displayed digitally Can Measure Volts, Ohms, Current, Frequency, Duty Cycle, Rpm Have a high impedance, safe on sensitive components and circuits Wide variety of adapters available Internally fused against overload

14. DVOM – Continued Common Prefixes used on meters: Mega (M) 1,000,000 Kilo (K) 1,000 Milli (m).001

15. DVOM - RULES Measuring voltage must be done on a live circuit Measuring resistance (ohms) must be dome on a dead circuit Measuring current flow (amps) must be done in series within the circuit