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Electricity: Properties, Ohm's Law, Circuits, Multimeters, Magnetic Fields

Explore the properties of electricity, learn about Ohm's Law, understand electrical circuits, use multimeters for measurements, and discover the effects of magnetic fields.

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Electricity: Properties, Ohm's Law, Circuits, Multimeters, Magnetic Fields

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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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