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Difficulty: MediumMultimeter: Resistance and Continuity

An automotive technician tests an unpowered single-pole single-throw (SPST) toggle switch that has been removed from a vehicle's dashboard. With the digital multimeter set to the resistance (Ω\Omega) mode and the switch set to the OFF position, what should the meter display across the switch terminals if the switch is functioning normally?

  1. An infinite resistance or "OL" (overload) reading, indicating an open circuitAnswer
  2. B
    A reading of approximately 0 Ω0\text{ }\Omega with a continuous beep, indicating a complete path for current
  3. C
    A constant reading of 12 V12\text{ V}, representing the supply voltage held across the open contacts
  4. D
    A reading of several kilo-ohms (kΩ\text{k}\Omega) that gradually drops to zero once the circuit is energized

Answer

An infinite resistance or "OL" (overload) reading, indicating an open circuit
When an SPST toggle switch is placed in the OFF position, its internal mechanical contacts are physically separated. This creates an open circuit with infinite electrical resistance. A digital multimeter set to resistance (Ω\Omega) or continuity mode will display this condition as "OL" (overload / open loop) or infinite resistance (∞\infty), confirming that no current can flow across the open terminals.

Step-by-Step Solution

1
Identify the physical state of the switch contacts in the OFF position
The internal mechanical contacts are physically separated (open)
An SPST switch in the OFF position interrupts the current path by creating an air gap between terminals.
2
Determine how a digital multimeter interprets an open path in resistance (Ω\Omega) mode
The meter measures infinite resistance, displayed as "OL" or "∞\infty"
An open circuit provides no path for the multimeter's internal sensing current to return.

Key Concept

Interpreting open circuit resistance readings on a digital multimeter
Estimated Time:1m 0s
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Topics

Multimeter: Resistance and Continuity

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