3 A student investigates how the period of a simple pendulum depends on its length. The period of a pendulum is the time for one complete swing (oscillation) of the pendulum. This is shown in Fig. 3.1, where the period is the time taken for the bob to swing from P to Q and back to P again. point of support PO pendulum bob Fig. 3.1 She sets up the pendulum as shown in Fig. 3.2. dh -clamp pendulum bob -bench Fig. 3.2 Fig. 3.2 is drawn to a scale of one-tenth full size. (a) (i) Measure the length I of the pendulum in Fig. 3.2 to the nearest 0.1 cm. length 1 = cm [1]7 (ii) Calculate the actual length , of the pendulum she uses. Record your answer below and in Table 3.1 in (b). actual length 4 = .. cm [1] (iii) The actual length , of the pendulum is the distance from the point of support to the centre of the pendulum bob. Describe a precaution that the student should take to measure , as accurately as possible. You may draw a diagram if you wish. [1](b) The student then moves the pendulum bob to position P and releases it so that it oscillates. She records the time taken for 20 oscillations. Fig. 3.3 shows the reading on the stopwatch. 00 : 30 . 98 Fig. 3.3 Record in Table 3.1 the reading on the stopwatch to three significant figures. [1] Table 3.1 LA/ cm time for 20 T2/$2 oscillations/s period T/s 50.0 28.4 1.42 2.0 40.0 25.4 1.27 1.6 30.0 22.0 1.10 1.2 20.0 18.0 0.90 0.8 She repeats the procedure described in (b) for lengths I of 50.0cm, 40.0cm, 30.0cm and 20.0cm. Her values are shown in Table 3.1. (c) Complete Table 3.1 by calculating the period 7 of the pendulum and T2 for the first set of results. Remember that the period is the time for one oscillation. [2]