In a simple circuit with one load, a voltmeter placed on the supply side would read which of the following?

• A. Reads full source voltage before the load and 0 volts after the load
• B. Reads 0 volts before and full after the load
• C. Reads the same voltage on both sides
• D. Reads half the source voltage on both sides

Answer: (C)

A voltmeter measures the difference in electric potential between its two leads, and it draws almost no current, so it doesn’t disturb the circuit. In a simple circuit with a single load, the source fixes a constant voltage between its two terminals. The wires have negligible resistance, so there is no extra voltage drop along the supply path. Whether you connect the voltmeter on the supply side or on the other side of the load, you are still measuring the same fixed potential difference provided by the source. That’s why the reading is the same on both sides.