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Chapter 1

Chapter 1. Properties of Electricity. Overview. What is Electricity Ohm’s Law Boat Circuit Problems Multimeters Magnetic Lines of Force. What is Electricity. Electricity consists of electrons Negatively charged Electrons actually flow from negative to positive

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Chapter 1

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  1. Chapter 1 Properties of Electricity

  2. Overview • What is Electricity • Ohm’s Law • Boat Circuit Problems • Multimeters • Magnetic Lines of Force

  3. What is Electricity • Electricity consists of electrons • Negatively charged • Electrons actually flow from negative to positive • Current “flow”, by convention, from positive to negative • Conductors have electrons that readily move • e.g. silver, copper, metal and liquids (salt water) • Insulation has tightly bonded electrons • Charges do NOT move • e.g. plastic, rubber, glass and ceramics

  4. Water Analogy • Height of water = Voltage • Valve = Switch • Water wheel = Electric motor • Small pipe = Resistance

  5. Electrical Circuits • Simple Series Circuit • Same current flow through all devices

  6. Complex Series Circuit • If one light bulb burns out… • No lights will be on • Therefore, not used for light circuits Off Off

  7. Complex Parallel Circuit • If one light bulb burns out… • Other will remain on • Therefore, used for light circuits On On

  8. Ohm’s Law • E = Voltage (pressure) in volts • I = Current (rate of flow) in amperes • R = Resistance (friction) in ohms • P = Power (work) in watts E = I * R R = E / I I = E / R P = I * E P = I2* R P = E2 / R E I R

  9. Practice (fig 1-5) • Given 12 volts and 4 amps • What is resistance? E = I * R R = E / I R = 12 / 4 R = 3 ohms (or 3 Ω) 12 VDC 4.0 Amps

  10. Practice (fig 1-6) RT = R1 + R2 • Given 12 volts and 8 ohms • What is current? E = I * R I = E / R I = 12 / 8 I = 1.5 amps 4 ohms (each) 12 VDC

  11. 2 Ohms 6 Ohms 6 Ohms Practice (fig 1-8) • What is current in each device? 6 amps in 2 ohms 2 amps in 6 ohms (each) • What is total current? IT = I1 + I2 + I2 IT = 10 amps 12 VDC

  12. Electrical Power • Watt is unit of electrical power • Given 12 VDC and total resistance of 6 Ω • What is total power? I = E / R I = 12 / 6 I = 2 amps P = E * I P = 12 * 2 P = 24 watts

  13. What We Have Learned So Far • Electricity is the negatively charged electrons that have been freed from the structure of an atom • For electricity to perform some useful function it must flow in a circuit • There are two basic types of electrical circuits • The Series Circuit • The Parallel Circuit • Using Ohm's Law we can calculate the three electrical values in a circuit, i.e. Voltage, Amperage, and Resistance • The fourth electrical value is Power • Power is measured in Watts • Using the PIE equation we can calculate Power • Using Ohm's Law and PIE equation if we know any two values we can find the other two

  14. Boat Circuit Problems • Open Circuit is “break” in electrical wiring • Current flow (path) is interrupted • Sometimes deliberately by switch • Short circuit is electrical wiring shortened from original length • Shorts to ground • Interwiring short • Internal short

  15. Multimeters • Used to measure • Voltage • Current • Resistance • Types of Multimeters • Analog • Digital • Preferred • Easier to read

  16. Measuring Voltage • Voltage to DC • Range to 20 volts • Red lead to positive • Black lead to negative • Meter across load • Parallel with load • Battery voltage is 12.6

  17. Measuring Voltage at Light • with good fuse • and switch “On” • Should measure approx. 12 VDC at each light

  18. Measuring Voltage Drop • Across a closed switch • Should measure zero volts • Across a high resistance “connection” • Should measure a voltage drop

  19. Measuring Current • Current to DC • Range to 10 amps • Red lead to current jack on multimeter • Insert meter in series with circuit When measuring voltage - meter is across the load

  20. Measuring Resistance • Function to resistance • Touch test leads together • Adjust resistance to zero (0.0) ohms • Place test leads across device to be measured • Continuity measurement • When test leads are across low resistance (Good circuit or device) • Will hear a buzz indicating continuity

  21. Magnetic Lines of Force • Results of Electrical Current • Heat (due to resistance in wire) • Chemical reaction (in current carrying solution) • Magnetic Field (illustrated)

  22. AWG#2 (Large Wire) AWG#16 (Small Wire) Remote Control Circuit Small current through solenoid coil - Controls larger current, through contacts, to Starter Motor

  23. Summary • Electricity is negatively charged electrons • Current flows from positive to negative • Types of circuits • Series (one path for current flow) • Parallel (multiple paths for current flow) • Ohm’s Law • E = I * R • P = E * I • Boat Circuit Problems • Open Circuits • Short Circuits

  24. Summary - 2 • Multimeter • Digital preferred • Measure voltage across (parallel to) load • Can also measure voltage drop • Measure current in series with load • Magnetic Lines of Force • Concentrated in coil • Solenoids use in remote control circuits • Small current controls large current

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