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Chapter 4

Chapter 4. The Simple Circuit and Ohm’s Law.

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Chapter 4

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  1. Chapter 4 The Simple Circuit and Ohm’s Law Conductors • Switches • Switch Characteristics • Loads • Overcurrent • Overcurrent Protection Devices • Voltage and Current Measurements • DC Voltage Measurements • DC Current Measurements • Ohm’s Law • Determining Current • Determining Voltage • Determining Resistance • Determining Power

  2. An electrical circuit consists of a voltage source, insulated conductors, a load, a switch, and a fuse.

  3. In a schematic or wiring diagram, conductors are shown as lines. Conductors that are connected often use a dot to indicate the connection.

  4. Switches are control devices and are used to close and open circuits safely.

  5. The position of the contacts, number of poles, number of throws, and type of break are used to describe switch contacts.

  6. Switches are available in many shapes and are often designated according to their use.

  7. Common lighting circuit switches include two-way, three-way, and four-way switches.

  8. Rotary switches are used to connect multiple positions to a single pole.

  9. Loads convert electrical energy to another form of energy such as motion, light, heat, or sound.

  10. A short circuit has a resistance that is lower than the normal circuit resistance.

  11. Overcurrent protection devices such as fuses are used to protect a circuit from a short circuit or overcurrent that can cause circuit damage.

  12. Cartridge and plug fuses may be surrounded with glass or encased in a composite material to suppress an arc or flame.

  13. A circuit breaker is an overcurrent protective device that does not need to be replaced each time the circuit current rating is exceeded. Circuit breakers may be thermally or magnetically operated.

  14. Thermal circuit breakers use a bimetallic strip attached to a latch mechanism to open the circuit when a short circuit or overload occurs.

  15. Magnetic circuit breakers use an electromagnet coil and armature to open the circuit when a short circuit or overload occurs.

  16. Thermal overload relay contacts open when the current level is exceeded for a given period of time. The temperature rise in the metal frame of the motor is used to heat the bimetallic strip.

  17. In a standard motor control circuit, a relay coil controls a set of normally open contacts and a set of normally closed overload relay contacts.

  18. DC voltage measurements using a digital multimeter are taken by connecting the black test lead to the negative polarity test point and the red test lead to the positive polarity test point.

  19. DC voltage is measured with an analog meter using standard procedures.

  20. To measure current flow through a component, a meter must be connected so that the total electron flow is through the meter circuit.

  21. DC current is measured with an analog multimeter using standard procedures.

  22. Clamp-on ammeters measure current by measuring the strength of the magnetic field around a single conductor.

  23. Ohm’s law is the relationship between voltage, current, and resistance in an electrical circuit.

  24. Current in a circuit increases with an increase in voltage and decreases with an increase in resistance.

  25. Voltage in a circuit increases with an increase in current and increases with an increase in resistance.

  26. Resistance in a circuit increases with an increase in voltage and decreases with an increase in current.

  27. The power formula is the relationship between power, voltage, and current in an electrical circuit.

  28. Power in an electrical circuit is calculated by multiplying current by voltage.

  29. Power in an electrical circuit calculated by multiplying current squared by resistance.

  30. Power in an electrical circuit can be calculated by dividing voltage squared by resistance.

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