What it shows
The pull of a magnet gets weaker as the gap between it and the steel grows. By stacking sheets between a magnet and a steel surface, you measure how quickly magnetic force falls with distance.
The science
The magnetic force on a steel surface drops quickly as the distance from the magnet rises. Each sheet of paper is about 0.1 mm thick and adds to the gap between the magnet and the steel. Paper is not magnetic, so it does not block the field, but the gap weakens the force a lot.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- 3 fridge magnets of different strengths
- A steel surface such as an almirah door or a steel plate
- Sheets of plain paper
- A thread and a small bag
- Paper clips or coins as weights
- A kitchen scale
- A notebook
Safety
For this project: Keep magnets away from phones, credit cards and anyone with a pacemaker. Do not swallow magnets and keep small ones from small children.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
7 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Stick a magnet on the steel surface and fix a thread loop to it with strong tape, so that a small bag can hang from the loop.
Add paper clips to the bag until the magnet slips off, and record the weight it held.
Place one sheet of paper between the magnet and the steel and repeat the load test.
Add two, four, eight and sixteen sheets and measure the holding load each time.
Record all values in a table, and test each of the three magnets.
Plot a graph of holding load against the number of sheets.
Find out the number of sheets at which the magnet can no longer hold itself up.
What you should see
The holding load falls as sheets are added, and each magnet fails at a different number of sheets. Stronger magnets work through more paper.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What happens to magnetic force with distance?
It falls rapidly.
02Does paper block magnetic force?
No, it only increases the gap.
03Which magnet is the strongest?
The one that holds the load through the most sheets.
04Why keep magnets away from phones?
They can interfere with some parts and cards.
Take it further
Use cloth or cardboard instead of paper and see if the thickness explains the results.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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