How do voltmeter readings differ with an open and closed switch? Where will they be more and where will they be less?

Consider two cases:
1) measuring the voltmeter readings on the circuit section.
2) measurement of voltmeter readings at the source of emf.

In the first case, the voltage will be only when the circuit is closed, i.e. when the switch is open, the voltmeter readings are zero.

In the second case, the voltmeter reading will be lower when the power supply is under load, i.e. when the circuit is closed. When the key is open, the voltmeter readings at the source of the emf will be slightly higher.