In this experiment, you will investigate the distance at which a bar magnet first attracts a small iron pin. You places the iron pin on a smooth, flat surfa...
Question 1 Report
In this experiment, you will investigate the distance at which a bar magnet first attracts a small iron pin. You places the iron pin on a smooth, flat surface at the zero mark of a metre rule. You slowly slides a bar magnet along the rule towards the pin, with the N pole leading. You records the distance between the N pole and the pin at the moment the pin first moves towards the magnet. You repeats the measurement five times. You then turns the magnet so the S pole leads and repeats five more trials. Fig. 8.1 shows the arrangement. Fig. 8.2 shows the ruler scale at the moment the pin first moves in one of the N-pole trials. Your results for the N pole are: 2.4, 2.5, 2.3, 2.4 and 2.6 cm. Your results for the S pole are: 2.3, 2.2, 2.4, 2.3 and 2.1 cm.
(a) Measure the distance shown on the ruler in Fig. 8.2. Record your value. [1]
(b) Record the mean distance for the N pole. Show your working. [2]
(c) State whether the N pole or the S pole has a greater reach. Use data from the results to support your answer. [2]
(d) Describe one difficulty in determining the exact moment the pin first moves. [1]
(e) Plan an experiment to investigate whether the reach of the magnet depends on the mass of the iron pin. State the independent variable, the dependent variable and two variables that must be kept constant. [3]
(f) Write a conclusion for you's experiment. [1]
Answer Details
(a) Distance from Fig. 8.2 [1]
The pin position arrow in Fig. 8.2 points to approximately 2.3 cm on the ruler scale (accept 2.2 to 2.4 cm). Each small division is 0.1 cm (the ruler has 10 divisions per cm).
(b) Mean distance for N pole [2]
\( \bar{d} = \frac{2.4 + 2.5 + 2.3 + 2.4 + 2.6}{5} = \frac{12.2}{5} = 2.44 \) cm [1]
Working shown with all five values added and divided by 5 [1].
(c) Which pole has greater reach? [2]
Mean for N pole = 2.44 cm. Mean for S pole: \( \frac{2.3 + 2.2 + 2.4 + 2.3 + 2.1}{5} = \frac{11.3}{5} = 2.26 \) cm.
The N pole has a slightly greater reach (2.44 cm vs 2.26 cm) [1]. However, the ranges overlap: N pole range is 2.3-2.6 cm, S pole range is 2.1-2.4 cm. Because of this overlap, the difference may not be significant and could be within experimental uncertainty [1]. For a true bar magnet, both poles have equal strength; any measured difference is likely due to experimental error.
(d) Difficulty in determining exact moment [1]
The initial movement of the pin is extremely small and difficult to observe. The pin may also vibrate slightly due to air currents, table vibrations, or the magnet's approach, making it hard to distinguish genuine magnetic attraction from incidental movement. Reaction time in stopping the magnet adds further uncertainty.
(e) Planning the investigation [3]
- Independent variable: mass of the iron pin (use pins of different masses) [1]
- Dependent variable: distance at which the pin first moves towards the magnet [1]
- Control variables (any two): same bar magnet and same pole (N or S) facing the pin; same smooth surface; same method of sliding the magnet; same ambient conditions (no nearby iron objects) [1]
(f) Conclusion [1]
The bar magnet attracts an iron pin from a distance of approximately 2.3 to 2.4 cm. The N pole and S pole attract the pin from similar distances, with no large or statistically significant difference between them. The magnetic field extends a short distance from either pole and exerts a measurable force on a small iron pin within that range.
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