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Unit 2 | Using tools, equipment and other devices

Unit 2 | Using tools, equipment and other devices. Lecturer: Mr. Jerome Smith Course: CAP. Basic Electric Circuits & Components. Introduction SI Units and Common Prefixes Electrical Circuits Direct Currents and Alternating Currents Resistors, Capacitors Ohm’s, Power Law

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Unit 2 | Using tools, equipment and other devices

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  1. Unit 2 | Using tools, equipment and other devices Lecturer: Mr. Jerome Smith Course: CAP

  2. Basic Electric Circuits & Components • Introduction • SI Units and Common Prefixes • Electrical Circuits • Direct Currents and Alternating Currents • Resistors, Capacitors • Ohm’s, Power Law • Power Dissipation in Resistors • Resistors in Series and Parallel • Resistive Potential Dividers • Sinusoidal Quantities • Circuit Symbols

  3. SI Units

  4. Common Prefixes

  5. Electrical Circuits • Electric charge • an amount of electrical energy • can be positive or negative • Electric current • a flow of electrical charge, often a flow of electrons • conventional current is in the opposite direction to a flow of electrons • Current flow in a circuit • a sustained current needs a complete circuit • also requires a stimulus to cause the charge to flow

  6. Section 7.2: Electric Current • Static Electricity: build up of charges that pass QUICKLY to another object • Electric Current: continuous flow of charges through a conductor

  7. Electromotive force and potential difference • the stimulus that causes a current to flow is an e.m.f. • this represents the energy introduced into the circuit by a battery or generator • this results in an electric potential at each point in the circuit • between any two points in the circuit there may exist a potential difference • both e.m.f. and potential difference are measured in volts

  8. A simple circuit • A water-based analogy

  9. Voltage • Voltage is created by • a chemical cell (battery) when it changes chemical energy to electrical energy • by a generator when it changes mechanical energy to electrical energy • by a solar cell when it changes light energy to electrical energy.

  10. Direct Current and Alternating Current • Currents in electrical circuits may be constant or may vary with time • When currents vary with time they may be unidirectional or alternating • When the current flowing in a conductor always flows in the same direction this is direct current (DC) • When the direction of the current periodically changes this is alternating current (AC)

  11. Resistors, Capacitors and Inductors • Resistors provide resistance • they oppose the flow of electricity • measured in Ohms () • Capacitors provide capacitance • they store energy in an electric field • measured in Farads (F)Forumlae: • Capacitors in Series: (1/CTOTAL) = (1/C1) + (1/C2) + (1/C3) Capacitors in parallel: CTOTAL = C1 + C2 + C3 ..... • Inductors provide inductance • they store energy in a magnetic field • measured in Henry (H)

  12. Check for Understanding • What is voltage? • How is voltage generated? (3 ways) • What is current?

  13. Resistance • Resistance: the tendency for a material to oppose the flow of electrons • Changes electrical energy into thermal energy and light • Ex: lightbulb filament • Resistance is measured in Ohms (Ω)

  14. What Affects Resistance?

  15. Household Circuits: Fuse: a small piece of metal that melts if the current becomes too high Circuit Breaker: contains a small piece of metal that bends when it gets hot bending causes a switch to flip and opens the circuit

  16. Ohm’s Law • The current flowing in a conductor is directly proportional to the applied voltage V and inversely proportional to its resistance R V = IR I = V/R R = V/I

  17. Power Law Power is the measure of how much work can be done in a given amount of time. • Did you know?1. W = V x I2. W = I2 x R ?3. W = V2 / R ? • Lets see!!

  18. Sinusoidal Quantities • Length of time between corresponding points in successive cycles is the periodT • Number of cycles per second is the frequency f • f = 1/T

  19. Circuit Symbols

  20. Key Points

  21. Let’s Compare Series and Parallel Circuits Series Circuits Parallel Circuits • _______ path(s) for current • Current ________________ • Voltage ________________ • Break in circuit _______________________ • Adding resistance in series ______________________ • _______ path(s) for current • Current ________________ • Voltage ________________ • Break in circuit _______________________ • Adding resistance in parallel _______________________

  22. Let’s Compare Series and Parallel Circuits Series Circuits Parallel Circuits • 1 path(s) for current • Current is the same at every point • Voltage drops at each resistor • Break in circuit stops all current • Adding resistance in series decreases total current (dimmer light bulbs) • multiple path(s) for current • Current can be different in each branch • Voltage same across each resistance • Break in circuit does not affect other bulbs • Adding resistance in parallel increases total current

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