In a circuit with an open switch, which statement is true?

• A. No voltage will exist anywhere in the circuit when the switch is open.
• B. The entire circuit still has the supply voltage when the switch is open.
• C. Only the supply side remains energised when the switch is open.
• D. There can be voltage present in at least part of the circuit when the switch is open.

Answer: (D)

When a circuit has an open switch, current stops because the path is interrupted, but the power source still creates a potential difference. That means voltage can exist at various points in the circuit even though no current is flowing. You could measure the full supply voltage across the open gap or on the side still connected to the source, while other parts may sit at different potentials. So it’s possible for voltage to be present in at least part of the circuit with the switch open.