In this experiment, you will compare how well an iron nail and a steel nail retain their magnetism over time. Both nails are the same length. You magnetises...
Question 1 Report
In this experiment, you will compare how well an iron nail and a steel nail retain their magnetism over time. Both nails are the same length. You magnetises each nail by stroking it 50 times with the same bar magnet in the same direction. Immediately after magnetising, you holds the tip of each nail above a pile of small iron pins and counts the number of pins that cling to the tip. You repeats the count at 1, 2, 3 and 5 minutes after magnetisation, leaving each nail undisturbed on the bench between counts. Fig. 5.1 shows the arrangement. Fig. 5.2 shows one of the nails alongside a ruler. Your results are in Table 5.1.
| Time after magnetisation / min | Pins picked up (iron nail) | Pins picked up (steel nail) |
|---|---|---|
| 0 | 8 | 8 |
| 1 | 4 | 8 |
| 2 | 2 | 7 |
| 3 | 1 | 7 |
| 5 | 0 | 7 |
(a) Record all the readings from Table 5.1. [1]
(b) Measure the length of the nail from the ruler in Fig. 5.2. Record your measurement. [1]
(c) Complete Table 5.1 by calculating the percentage of initial strength retained at 5 minutes for each nail. Record your values. [1]
(d) Use the grid to draw graphs of pins picked up (y-axis) against time (x-axis) for both the iron nail and the steel nail on the same axes. Draw smooth curves of best fit. Label each curve. [3]
(e) Describe the difference in behaviour between the iron nail and the steel nail. [1]
(f) State which nail is made of a magnetically hard material. Explain your answer. [2]
(g) Explain why both nails must be stroked the same number of times. [1]
(h) Give one practical use of a magnetically hard material. [1]
Answer Details
(a) Recording readings [1]
All readings from Table 5.1 should be recorded: at 0 min, iron = 8, steel = 8; at 1 min, iron = 4, steel = 8; at 2 min, iron = 2, steel = 7; at 3 min, iron = 1, steel = 7; at 5 min, iron = 0, steel = 7.
(b) Length of nail [1]
From the ruler in Fig. 5.2, the nail extends from 0.5 cm to 7.0 cm (approximately). Length = 6.5 cm (accept 6.4 to 6.6 cm).
(c) Percentage of initial strength retained at 5 minutes [1]
- Iron nail: \( \frac{0}{8} \times 100 = 0\% \)
- Steel nail: \( \frac{7}{8} \times 100 = 87.5\% \) (accept 88%)
The iron nail has lost all its magnetism, while the steel nail retains nearly all of it.
(d) Graph [3]
[1] Both sets of points plotted correctly on the same axes (pins picked up on y-axis, time / min on x-axis). [1] Smooth curves of best fit drawn for each dataset. [1] Each curve is clearly labelled as "iron" or "steel". The iron curve drops steeply from 8 to 0, while the steel curve remains nearly flat at 7-8.
(e) Difference in behaviour [1]
The iron nail loses its magnetism rapidly: from 8 pins at time zero to 0 pins after 5 minutes. The steel nail retains most of its magnetism, still holding 7 pins after 5 minutes. Iron is easily magnetised but easily demagnetised (magnetically soft), while steel holds its magnetism (magnetically hard).
(f) Which nail is magnetically hard? [2]
The steel nail is made of a magnetically hard material [1]. A magnetically hard material retains its magnetism once the magnetising field is removed. The steel nail's magnetic domains remain aligned after stroking, so it continues to attract pins over time, as shown by the nearly constant pin count [1].
(g) Why stroke both nails the same number of times [1]
Both nails must receive the same initial magnetisation so that the experiment is a fair test. If one nail were stroked more times, it might start with a stronger magnetic field. Any difference in how long the magnetism lasts must be due to the material's magnetic properties, not to how strongly it was magnetised initially.
(h) Practical use of magnetically hard material [1]
Any one valid example: permanent magnets (e.g. fridge magnets), compass needles, magnetic door catches, loudspeaker magnets, or electric motor magnets. These applications require the magnet to retain its field permanently without an external magnetising current.
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