Question

A complete series circuit consists of a 12.0 V battery, a 4.70 O resistor, and a switch. The internal resistance of the battery is 0.30 O. The switch is open. What does an ideal voltmeter read when placed across the terminals of the switch?

12.0 V
9.40 V
2.40 V
zero

Answer 1

With the switch open, there's no current in the circuit, and therefore
no voltage drop across any of the dissipative elements (the resistor
or the battery's internal impedance). So the entire battery voltage
appears across the switch, and the voltmeter reads 12.0V .