The diagram illustrates a circuit made up of a cell, two resistors, a switch and a voltmeter. With the switch open, the voltmeter shows $1.5\,\text{V}$. With the switch closed, the voltmeter shows $2.0\,\text{V}$. What is the electromotive force (e.m.f.) of the cell?
- A$0.5\,\text{V}$
- B$1.5\,\text{V}$
- C$2.0\,\text{V}$
- D$3.5\,\text{V}$