The diagram below shows a practical cell with electromotive force (emf) ε \varepsilon\,ε and internal resistance rrr, connected to an external resistor R R\,R via a switch SSS. A high-resistance voltmeter V V\,V is connected across the terminals of the practical cell.
Which of the following describes the conditions required for a continuous electric current I I\,I to flow through the external resistor RRR, and the correct relationship for the reading on the voltmeter V V\,V once this current is flowing?
The switch SSS must be open, and the voltmeter reading is V=εV = \varepsilonV=ε.
The switch SSS must be closed, and the voltmeter reading is V=ε−IrV = \varepsilon - IrV=ε−Ir.
The switch SSS must be closed, and the voltmeter reading is V=ε+IrV = \varepsilon + IrV=ε+Ir.
The switch SSS must be open, and the voltmeter reading is V=0V = 0V=0.