Varying strength on electromagnets (2 Viewers)

[lazylol]

We have to design a electromagnet in which settings can be changed to pick up an increasing amount of weight i.e. it can pick up 50 grams but not 100 grams, and then 100g but not 150g. We cannot change the voltage, the current, the resistance or the number of coils. The only variable left I can think of is the length and size of metal within the coils. Is this the only option left?

And also where can I buy insulated copper wire? I'm not sure how to connect the wire and battery either... I feel like such a physics noob. :S

Any help would be enormously appreciated! Thanks

 

[Toranilor]

The factors affecting the strength of electromagnet strenght are, to quote the internet;

"The temperature, current, length of the core, diameter, the thickness of the
wire used for the coils, how tightly the coils of wire are wrapped around,
the material and also the number of turns on the electromagnet."

Seeing as you can't change turn numbers, current, voltage or resistance, that leaves you with core length, diameter, wire size and coil tightness.

What I'd reccomend doing is having two ferromagnetic cores that you can substitute for one another to produce different strength.

Hope that helps.

 

[lazylol]

The problem I have is that I need to be able to change magnet strength in a really short period of time because I am testing 50g and then the 100g, 150g, 200g and 250g. And the magnet strength has to increase each time which means I will have to change the core 4 times...

Your suggestion on coil tightness seems my best bet. Need to do some more research. Thanks a lot