Lab #2 – Magnets
Purpose: By now we are very familiar with electrostatics and have even had a taste of electrodynamics (effects produced from the continuous moving of charges). Now we move onto another fundamentally bizarre phenomenon: magnetism.
Again it was the ancient Greek philosopher Thales who noticed that certain stones from the region of Magnesia in Asia Minor were capable of attracting iron. These stones became known as “magnetite,” and their unusual property was termed “magnetism.” Fascinated with the attractive force of magnetite, Ptolemy Philadelphos of Egypt plated the entire surface of a temple with it, vainly hoping to suspend an iron idol of himself in mid-air. It was noticed that magnetite oriented in a north/south direction, and inventors in both China (quite early on) and Italy (much later, in the 12th century) capitalized on this property to develop the magnetic compass, one of the key inventions that made the Age of Exploration possible and forever changed the course of history. By the 1500’s, Europeans employed compass navigation as they set sail to explore and colonize Africa, Asia, Australia, North America, South America, and the islands of the Pacific.
Part 1 – Properties of Magnets
- Obtain one magnet and a few paperclips. Touch the tip of a paperclip to a magnet. Does it ‘stick’? Now touch the tip of another paperclip to the other end of the stuck paperclip. Does the second paperclip stick to the first? See how many paperclips you can string together before the sticking force ‘runs out’.
- Now take two magnets. While keeping them from touching, hold one in each hand and move them towards each other. Try this a few more times, but re-orient the magnets so that different parts of the magnets face each other as you bring them near.
- Take a piece of blank white paper. Pour a small amount of iron filings onto the paper. (Note: these iron filings need to be saved, so please be careful not to spill them.) Place one magnet on the table in front of you, and hold the sheet of paper so the iron filings are suspended about 6 inches above the magnet. Have a partner gently tap the paper from above a few times. Note any patterns that form.
- Now move the sheet of paper about an inch closer to the magnet and have your partner tap the paper a few times again. Note any patterns.
- Repeat this process of lowering the sheet of paper so that it is closer to the magnet, then having someone tap the paper a few times.
- Allow the paper to touch the magnet. Note the tendency of the iron filings to form very specific patterns.
- Now move the magnet underneath the paper and observe the effects upon the iron filings as you do so. Flip it, rotate it, turn it on end, etc.
- Obtain a “magnaprobe” and use it to explore in detail the ‘field’ of the magnet. You will use the information from Part 1 to help you draw this field for your MLB.
Part 2 – Creating a Magnet
- Take a 6” nail, and touch it to a paper-clip.
- Using one magnet, identify the part of the magnet that attracts the nail most strongly. Then take the magnet in one hand and the nail in the other, and stroke the magnet along the nail from the head all the way to its tip with the part of the magnet you identified as having the greatest attractive effect. Make sure that you stroke the magnet from the head to the tip every single time, removing the magnet from the nail between strokes. Do this 50 times. Now touch the tip of the nail to a paper-clip. Does it ‘stick’?
- See how many paper-clips can be suspended end-to-end with your nail.
- Try suspending paper-clips from other places on your nail: the middle, the other end, etc.
- Now place your nail on the ground and hit it with the hammer 5 or 6 times. Do not hit the nail so hard that it actually bends or changes shape – the nails will be re-used. Now see how many paper-clips your nail will hold after being struck.
- Re-magnetize your nail by repeating step 11. Verify that it is magnetized by picking up some paper-clips with it. Now obtain a miniature compass, and bring the tip of the nail towards the compass. Note which end of the compass is attracted to the tip of the nail. Now bring the opposite side of the nail, the head, towards the compass, noting which end of the compass is attracted to the head of the nail.
- Now obtain a piece of string, and tie it around the center of your nail so that when you suspend the nail by the string it hangs exactly horizontally. Tie your string to something so that the nail hangs away from any other magnetic sources in a place where it will not be accidentally bumped for at least ten minutes. Leave your nail suspended for ten minutes without disturbing it in any way.
Questions to consider for your write-up:
- Come up with a list (with discussion if necessary) of similarities and differences that exist between the magnetic and electric forces.
- Try and make a drawing of the magnetic field around a magnet (use your observations about the iron filings to help you visualize it).
- Could you suspend more than one paperclip from a magnet when the paperclips were not themselves magnetized?
- Why does it matter which direction you stroke the nail with in order to magnetize it?
- Why might hitting your nail with a hammer ‘demagnetize’ it?
- What might it mean that a magnetized and suspended nail points in a certain direction? Why might this happen?
- Can you “feel” a magnet when it is near you like you could feel the effect of a charged rod?
- Come up with two of your own questions about any part of these experiments and the magnetic force. Try to think of a plausible experiment that would help answer each question.