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Understanding Electricity Current and Voltage in Circuits

Learn about electric current and voltage in circuits, including measurements, types of currents, and circuit configurations. Understand the basics of electrical pressure and flow.

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Understanding Electricity Current and Voltage in Circuits

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  1. Chapter 3 Electricity, Components and Circuits

  2. Electricity Current and Voltage. • Electrons are negatively-charged atomic particles. • Electric current is the flow of electrons through a material.

  3. Electricity Current and Voltage. • The magnitude of a current is the number of electrons flowing past a given point in one second. • Measured in amperes. • 1 Ampere = 1 coulomb/second. • 1 coulomb ≈ 6.24 billion billion (6.24 x 1018) electrons. • Abbreviated to ”Amp” or “A”. • Use symbol “I” in formulas. • Current is measured using an ammeter.

  4. Electricity Current and Voltage. • Voltage is the electrical force that causes electrons to flow. • a.k.a. – Electromotive force (EMF) or potential. • Measured in volts. • Abbreviated to “V” • Use symbol “E” in formulas • Voltage is measured using a voltmeter.

  5. Electricity Current and Voltage. • Voltage has polarity. • Positive voltage attracts electrons. • Negative voltage repels electrons. • Voltage is always referenced between 2 points. • Surface of the earth is often used as a universal reference point. • Called earth ground, ground potential, or ground.

  6. Electricity Current and Voltage. • Direct and alternating current. • A current where the electrons always flow in the same direction is called a direct current (DC). • A current where the direction the electrons are flowing reverses is called an alternating current (AC). • A voltage that always has the same polarity is called a direct voltage (VDC). • A voltage where the polarity changes is called an alternating voltage (VAC).

  7. T5A01 -- Electrical current is measured in which of the following units? • Volts • Watts • Ohms • Amperes

  8. T5A03 -- What is the name for the flow of electrons in an electric circuit? • Voltage • Resistance • Capacitance • Current

  9. T5A04 -- What is the name for a current that flows only in one direction? • Alternating current • Direct current • Normal current • Smooth current

  10. T5A05 -- What is the electrical term for the electromotive force (EMF) that causes electron flow? • Voltage • Ampere-hours • Capacitance • Inductance

  11. T5A09 -- What is the name for a current that reverses direction on a regular basis? • Alternating current • Direct current • Circular current • Vertical current

  12. T5A11 -- What is the unit of electromotive force? • The volt • The watt • The ampere • The ohm

  13. T7D01 -- Which instrument would you use to measure electric potential or electromotive force? • An ammeter • A voltmeter • A wavemeter • An ohmmeter

  14. T7D04 -- Which instrument is used to measure electric current? • An ohmmeter • A wavemeter • A voltmeter • An ammeter

  15. Electricity Circuits. • A circuit is any path where current can flow. • For current to flow, the circuit must be closed. • Current eventually ends up back where it started. • If only one path, it is a series circuit. • Same current flows through all components. • If multiple paths, it is a parallel circuit. • Same voltage is across all components.

  16. Electricity Circuits. • Electrical pressure and flow. • The flow of water through a hose is a good analogy to understand the characteristics of electricity and how they are related.

  17. Electricity Circuits. • Series circuit. • The voltage across each component varies depending on the type and value of each component. • The sum of all voltages around the circuit is zero. • The same current flows through all components.

  18. Electricity Circuits. • Parallel circuit. • The voltage across each component is the same. • The sum of all currents in each component equals the total current. • The current at the junction of 2 components varies depending on the type and value of each component.

  19. Electricity Circuits. • Measuring voltage and current. • Voltmeters are always placed in parallel with the circuit. • Ammeters are always placed in series with the circuit.

  20. T5A13 -- In which type of circuit is current the same through all components? • Series • Parallel • Resonant • Branch

  21. T5A14 -- In which type of circuit is voltage the same across all components? • Series • Parallel • Resonant • Branch

  22. T5D13 -- What happens to current at the junction of two components in series? • It divides equally between them • It is unchanged • It divides based on the on the value of the components • The current in the second component is zero

  23. T5D14 -- What happens to current at the junction of two components in parallel? • It divides between them dependent on the value of the components • It is the same in both components • Its value doubles • Its value is halved

  24. T5D15 -- What is the voltage across each of two components in series with a voltage source? • The same voltage as the source • Half the source voltage • It is determined by the type and value of the components • Twice the source voltage

  25. T5D16 -- What is the voltage across each of two components in parallel with a voltage source? • It is determined by the type and value of the components • Half the source voltage • Twice the source voltage • The same voltage as the source

  26. T7D02 -- What is the correct way to connect a voltmeter to a circuit? • In series with the circuit • In parallel with the circuit • In quadrature with the circuit • In phase with the circuit

  27. T7D03 -- How is a simple ammeter connected to a circuit? • In series with the circuit • In parallel with the circuit • In quadrature with the circuit • In phase with the circuit

  28. Electricity The Multimeter. • The most basic piece of test equipment. • Everybody should have one. • Three (or more) instruments in one: • Voltmeter • Ammeter • Ohmmeter • Measures volts, amperes, and ohms in one package.

  29. Electricity The Multimeter. • Digital multimeter (DVM) • Very inexpensive. • Often has extra features in addition to measuring volts, amps, & ohms.

  30. Electricity The Multimeter. • Meters can only measure current. • A voltmeter measures voltage by: • Placing a known resistance in parallel with the voltage being measured. • Measuring the current through the known resistance. • Calculating the voltage using Ohm’s law. • An ohmmeter measures resistance by: • Applying a known voltage to the circuit being measured. • Measuring the resulting current. • Calculating the resistance using Ohm’s law.

  31. Electricity The Multimeter. • Measuring resistance. • NEVER attempt to measure resistance with power applied to the circuit. • You WILL damage your multimeter. • NEVER attempt to measure voltage with the resistance setting. • You WILL damage your multimeter.

  32. Electricity The Multimeter. • When measuring high voltages, make certain that the voltmeter and the test leads are rated for the voltage being measured. • If a resistance reading is initially very low but slowly increases to a higher value, it indicates the presence of a large capacitance in the circuit.

  33. T7D06 -- Which of the following might damage a multimeter? • Measuring a voltage too small for the chosen scale • Leaving the meter in the milliamps position overnight • Attempting to measure voltage when using the resistance setting • Not allowing it to warm up properly

  34. T7D07 -- Which of the following measurements are commonly made using a multimeter? • SWR and RF power • Signal strength and noise • Impedance and reactance • Voltage and resistance

  35. T7D10 -- What is probably happening when an ohmmeter, connected across an unpowered circuit, initially indicates a low resistance and then shows increasing resistance with time? • The ohmmeter is defective • The circuit contains a large capacitor • The circuit contains a large inductor • The circuit is a relaxation oscillator

  36. T7D11 -- Which of the following precautions should be taken when measuring circuit resistance with an ohmmeter? • Ensure that the applied voltages are correct • Ensure that the circuit is not powered • Ensure that the circuit is grounded • Ensure that the circuit is operating at the correct frequency

  37. T7D12 -- Which of the following precautions should be taken when measuring high voltages with a voltmeter? • Ensure that the voltmeter has very low impedance • Ensure that the voltmeter and leads are rated for use at the voltages to be measured • Ensure that the circuit is grounded through the voltmeter • Ensure that the voltmeter is set to the correct frequency

  38. Electricity Resistance and Ohm’s Law. • Resistance • The opposition to the flow of electrons. • All materials exhibit resistance. • Materials with low resistance are called conductors. • Materials with high resistance are called insulators. • Unit of measurement is the Ohm (Ω). • Measured with an ohmmeter.

  39. T5A07 -- Which of the following is a good electrical conductor? • Glass • Wood • Copper • Rubber

  40. T5A08 -- Which of the following is a good electrical insulator? • Copper • Glass • Aluminum • Mercury

  41. T7D05 -- What instrument is used to measure resistance? • An oscilloscope • A spectrum analyzer • A noise bridge • An ohmmeter

  42. Electricity Resistance and Ohm’s Law. • First published in 1827 by Georg Ohm in his book “Die galvanischeKette, mathematischbearbeitet ” • Mathematically describes the relationship between voltage, current, and resistance. • Most basic formula in electricity and electronics.

  43. Electricity Resistance and Ohm’s Law. • E = Electromotive Force • Force causing electrons to flow. • I = Current Intensity • Number of electrons flowing past a point in a given period of time. • R = Resistance • Opposition to flow of electrons. E = I x R I = E/R R = E/I

  44. T5D01 -- What formula is used to calculate current in a circuit? • Current (I) equals voltage (E) multiplied by resistance (R) • Current (I) equals voltage (E) divided by resistance (R) • Current (I) equals voltage (E) added to resistance (R) • Current (I) equals voltage (E) minus resistance (R)

  45. T5D02 -- What formula is used to calculate voltage in a circuit? • Voltage (E) equals current (I) multiplied by resistance (R) • Voltage (E) equals current (I) divided by resistance (R) • Voltage (E) equals current (I) added to resistance (R) • Voltage (E) equals current (I) minus resistance (R)

  46. T5D03 -- What formula is used to calculate resistance in a circuit? • Resistance (R) equals voltage (E) multiplied by current (I) • Resistance (R) equals voltage (E) divided by current (I) • Resistance (R) equals voltage (E) added to current (I) • Resistance (R) equals voltage (E) minus current (I)

  47. T5D04 -- What is the resistance of a circuit in which a current of 3 amperes flows through a resistor connected to 90 volts? • 3 ohms • 30 ohms • 93 ohms • 270 ohms

  48. T5D05 -- What is the resistance in a circuit for which the applied voltage is 12 volts and the current flow is 1.5 amperes? • 18 ohms • 0.125 ohms • 8 ohms • 13.5 ohms

  49. T5D06 -- What is the resistance of a circuit that draws 4 amperes from a 12-volt source? • 3 ohms • 16 ohms • 48 ohms • 8 ohms

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