Chapter P1: Practical skills at AS level
3 It is suggested that two quantities T and x are related by the formula: T2 = kx where k is a constant. This table shows values of T and x: T/s
x / cm
2.0
4.00
6.3
41.3
a Use data from the table to calculate two values for k. b The uncertainty in each value of T is Âą 0.1 s. The uncertainty in x is very small. Calculate the percentage uncertainty in the smallest value of T. c State a criterion you can use to determine whether the data supports the relationship. d Explain whether the data supports the suggested relationship. 4 In this question you will need to describe sources of uncertainty and improvements in a basic experiment. Many such sources of uncertainty or limitations in the procedure will depend on the actual apparatus used. You may have to look up the apparatus in your textbook. For each situation described: â—?
imagine that you have taken two sets of readings of two quantities that are related; you have used your readings to see whether a suggested relationship is supported by these readings (remember that in any formula, k represents a constant)
â—?
suggest sources of error or limitations and then suggest improvements to reduce the errors or limitations.
a A metre rule is balanced on a pivot and two masses, one either side of the pivot. You check the relationship clockwise moment = anticlockwise moment. b You check that resistance R of a wire of constant length is related to the area of cross-section A using the relationship R = k / A. c A hacksaw blade is clamped at one end. You check that the period of oscillation t is related to the length l of the hacksaw blade that is free to vibrate, using the relationship t2 = k l3. d You check that the width w of a piece of paper tape is related to the maximum force F needed to break the tape when it is pulled by a newtonmeter, using the relationship F = kw.
Exam-style questions 1 A student connects a resistor of resistance R to a cell, as shown in this circuit diagram: E
r
I
I
R
The e.m.f. of the cell is E and its internal resistance is r. The current I is measured by an ammeter, which is not shown.
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