Two students do an experiment to determine the resistance per unit length of a metal wire. Student A uses a metre ruler to make a single measurement of the length of the wire She records a value of 625 mm. She measures the resistance of the wire as 5.3 ± 0.3 0. Show that the percentage uncertainty in the length of the wire is approximately 0.2%. Determine, in 2 m, the student's value for resistance per unit length and the absolute uncertainty in her calculated value. Student B determines values of resistance R for a range of lengths / for the wire and uses them to plot a graph.

Determine, using the gradient of the graph, the resistance per unit length of the wire in ohms -1 The method used by student B is better than the method used by student A.Suggest two reasons why