Why Is Magnetism Stronger at the Tip of a Tapered Blade?

[feynomite]

I have a pair of scissors. The blade is about 1.5 cm wide on one end (near the handle), and it tapers down to nothing after about 7-8cm. The blades are about 3mm in thickness. It's been magnetized, meaning, I guess, I've stuck a magnet on it a few times. I'm exactly sure how or why there is such a lasting residual effect, or how to get rid of it, but that's another topic.

Anyway, when I take something magnetic, like a stainless steel keychain ring, and hold it near the scissors, it is magnetically attracted much more so at the very tip of the scissors rather than anywhere else on the blade. I can tell this by feeling how hard I have to pull to get the keychain away from the scissors. It's much harder to lift it when its stuck to the tip than it is if its just a couple of cm away from the tip. Near the base of the blade it's barely attracted at all. The same applies to the edges of the blade.. it's not attracted to the edge of the blade unless its near the tip.

I wonder, how can the shape of the blade make it more magnetic on one end than the other? What would happen if I made the tip of the blade extremely narrow, would it become infinitely magnetic? Does the blade thickness factor into this, as well?

Thank you all for your input :)

 

[marcusl]

The scissors are magnetized along their length, just like a bar magnet. The magnetic lines of force travel along the metal and exit at the ends, which is why you feel the greatest force there. Here is a diagram showing the concentration of lines at the magnet ends ("poles").
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.html"

 

[astrokreng]

I find this observation of magnetism on a tapered surface to be very interesting. First of all, it is important to understand that magnetism is a result of the alignment of magnetic domains within a material. When a magnet is brought near a material, it can cause the magnetic domains to align in a certain direction, resulting in an attraction between the two.

In the case of your scissors, the fact that the magnetism is strongest at the tip is likely due to the shape of the blade. The tapered shape of the blade means that there is a smaller surface area at the tip compared to the base. This means that the magnetic field from the magnet is concentrated in a smaller area at the tip, resulting in a stronger attraction.

Additionally, the thickness of the blade may also play a role. Thicker materials tend to have stronger magnetic properties, so the 3mm thickness of your scissors may contribute to the overall strength of the magnetism.

Now, to address your question about making the tip of the blade extremely narrow - this would not necessarily result in an infinitely magnetic tip. While it may increase the concentration of the magnetic field at the tip, there is a limit to how much the magnetic domains can align. At some point, the material would reach its maximum magnetic strength and any further narrowing would not have a significant effect.

Overall, this is a fascinating observation and it highlights the importance of considering the shape and thickness of materials when studying their magnetic properties. Thank you for sharing your observation and sparking this discussion.