Topic Menu

Cyber-chess a chess instruction site

 

Questions on EMF and internal resistance

 

Q5. A battery of EMF and internal resistance r is connected in series to a variable resistor R and an ammeter of negligible resistance. A voltmeter is connected across R, as shown in the diagram.

(a)

(i) State what is meant by the EMF of the battery.

 

(ii) The reading on the voltmeter is less than the EMF. Explain why this is so.

(3)

(b) A student wishes to measure and r. Using the circuit shown above, the value of R is decreased in steps, and at each step the readings V and I on the voltmeter and ammeter respectively are recorded.

These are shown in the table below.

reading on voltmeter/V
reading on ammeter/A
8.3
0.07
6.8
0.17
4.6
0.33
2.9
0.44
0.3
0.63

(i) Give an expression relating V, I, and r.

(ii) Draw a graph of V (on the y-axis) against I (on the x-axis) on graph paper.

(iii) Determine the values of and r from the graph, explaining your method.

(9)

(Total 12 marks)