What will a voltmeter read if properly connected across a closed switch in a circuit with electrical power on?

What will a voltmeter read if properly connected across a closed switch in a circuit with electrical power on?

• A. Zero volts
• B. Full supply voltage
• C. Negative voltage
• D. Undefined

Answer: (A)

A voltmeter measures the difference in electrical potential between two points. When a switch is closed, it creates a direct, low-resistance path between its two terminals, effectively making both points sit at the same potential. Even though the circuit is powered, there’s no significant voltage drop across that short, so the meter reads zero volts. In practice, tiny resistance in the switch or wires could cause an extremely small reading, but it’s essentially zero. If the switch were open, you would see the full supply voltage across the gap, but with it closed, the reading is zero.

A voltmeter measures the difference in electrical potential between two points. When a switch is closed, it creates a direct, low-resistance path between its two terminals, effectively making both points sit at the same potential. Even though the circuit is powered, there’s no significant voltage drop across that short, so the meter reads zero volts. In practice, tiny resistance in the switch or wires could cause an extremely small reading, but it’s essentially zero. If the switch were open, you would see the full supply voltage across the gap, but with it closed, the reading is zero.