 # Questions on EMF and internal resistance Q6.

(a) In the circuit shown in the diagram the battery has an EMF of 6.0 V. With the switch closed and the lamp lit, the reading on the voltmeter is 5.4 V. Explain without calculation, why the voltmeter reading is less than the EMF of the battery.

(3)

(b) A torch is powered by two identical cells each having an EMF of 1.5 V and an internal resistance r. The cells are connected in series. The torch bulb is rated at 1.6 W and the voltage across it is 2.5 V.

(i) Draw the circuit described.

(ii) Calculate the internal resistance of each cell.

(5)

(c) In the circuit below the cell has emf and internal resistance r. The voltage V across the cell is read on the voltmeter which has infinite resistance, and the current I through the variable resistor R is read on the ammeter. By altering the value of the variable resistor R, a set of values of V and I is obtained. These values, when plotted, give the graph shown below. Show how the values of and r may be obtained from this graph. Explain your method.

(Total 11 marks)