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Difficulty: EasyMultimeter: Voltage and Current Measurement

An apprentice technician needs to measure the direct-current (DC) voltage drop across an operational auxiliary lamp in a 12 V12\text{ V} automotive circuit. Which procedure correctly connects the digital multimeter to take this measurement?

  1. A
    Connect the multimeter test leads in series by opening the circuit wire leading into the lamp.
  2. B
    Connect the multimeter in series with the power source while set to the direct-current amperage (DCA) function.
  3. Connect the multimeter test leads in parallel across the terminals of the energized lamp.Answer
  4. D
    Connect the multimeter in parallel across the lamp while set to the alternating-current voltage (ACV) mode.

Answer

Connect the multimeter test leads in parallel across the terminals of the energized lamp.
To measure the voltage drop across any electrical component, the multimeter must be set to DC Volts and connected in parallel across the component terminals while power is applied. A voltmeter has very high internal resistance, allowing it to measure potential difference without significantly altering circuit current.

Step-by-Step Solution

1
Identify the type of electrical measurement and electrical supply.
The measurement is potential difference (voltage) in a DC automotive circuit.
Multimeter meter dials must be set to DC Volts (DCV) rather than AC Volts or current settings.
2
Determine the proper probe connection orientation for a voltmeter.
Place the red positive lead on the positive terminal and the black COM lead on the negative terminal across the component.
Voltmeters possess extremely high internal resistance and measure the potential difference across two points, requiring a parallel hookup without breaking the circuit.

Key Concept

Voltage measurement across a load requires a parallel connection in DC mode without interrupting the circuit.
Estimated Time:45s
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Topics

Multimeter: Voltage and Current Measurement

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