1. A magnetized needle is oscillating on a string about a vertical axis in a horizontal magnetic field B. The time for 10 oscillations is recorded for different values of B.
The graph shows the variation with B of the time for 10 oscillations together with the uncertainties in the time measurements. The uncertainty in B is negligible.
(a) Draw on the graph the line of best fit for the data.
(b) (i) Write down the time taken for one oscillation when B = 0.005 T with its absolute uncertainty.
(ii) A student forms a hypothesis that the period of one oscillation P is given by:P/K√B
where K is a constant.
Determine the value of K using the point for which B = 0.005 T.State the uncertainty in K to an appropriate number of significant figures.
(iii) State the unit of K.
(c) The student plots a graph to show how P2 varies with 1/B for the data.
Sketch the shape of the expected line of best fit on the axes below assuming that the relationship P=K/√B is verified. You do not have to put numbers on the axes.
(d) State how the value of K can be obtained from the graph.
2. An experiment to find the internal resistance of a cell of known emf is to be set.The following equipment is available:
(a) Draw a suitable circuit diagram that would enable the internal resistance to be determined.
(b) It is noticed that the resistor gets warmer. Explain how this would affect the calculated value of the internal resistance.
(c) Outline how using a variable resistance could improve the accuracy of the value found for the internal resistance.