a) Internal resistance

cii) techniques and procedures used to determine the internal resistance of a chemical cell or other source of e.m.f.

to determine the internal resistance and the e.m.f. of an e.m.f. source

practical

• construct a circuit with a cell and variable resistor

  • with an ammeter connected in series to the circuit and a voltmeter connected in parallel to the cell

• use the variable resistor to change the resistance and give increasing current readings with regular intervals

• measure and note the current and p.d. for every resistance change

analysis

• rearrange ε = V + Ir into the form y = mx + c to get V = -rI + ε

• graph the data where the y-axis represents p.d. (V) and the x-axis represents current (I)

• gradient = negative internal resistance (-r), y-intercept = e.m.f. (ε)