When checking voltage across a closed switch, the voltmeter will normally show 120v.

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Multiple Choice

When checking voltage across a closed switch, the voltmeter will normally show 120v.

When a switch is closed, it essentially creates a short between the two conductors it connects. A voltmeter measures the potential difference between two points, and with a closed switch those two points are at nearly the same voltage. The only voltage drop comes from tiny contact resistance at the switch terminals, which is typically a few millivolts, effectively zero for practical purposes. So you won’t normally read 120 volts across a closed switch; you’ll read near 0 volts. If the switch were open, you could see the full supply voltage across the gap, depending on how the circuit is arranged, but that’s the opposite situation.

When a switch is closed, it essentially creates a short between the two conductors it connects. A voltmeter measures the potential difference between two points, and with a closed switch those two points are at nearly the same voltage. The only voltage drop comes from tiny contact resistance at the switch terminals, which is typically a few millivolts, effectively zero for practical purposes. So you won’t normally read 120 volts across a closed switch; you’ll read near 0 volts.

If the switch were open, you could see the full supply voltage across the gap, depending on how the circuit is arranged, but that’s the opposite situation.

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