# B Bar magnet wrapped in electromagnetic coil

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1. May 21, 2017

### coinmaster

If I wrap a coil around a bar magnet and shoot current through the coil so that the magnetic field of the electromagnet is at the same polarity of the bar magnet will I have amplified the magnetic field of the bar magnet maintaining the same magnetic shape but bigger/stronger?

2. May 21, 2017

### marcusl

No. A permanent magnet has a saturated magnetization (it is called "remanent magnetization" on the material's hysteresis curve). Applying additional field will simply add the field of the coil to the field of the magnet.

3. May 22, 2017

### coinmaster

Does that mean the field will be stronger but not bigger?

4. May 22, 2017

### marcusl

"Stronger" vs. "bigger" doesn't make sense. The field is stronger--it's the sum of the permanent magnetization and the applied solenoidal field. There is no "amplification," used in the sense that a ferromagnetic material produces a strong B field in the presence of a weak H field.

5. May 22, 2017

### coinmaster

Could I practically double the strength of a 4''x 0.5'' 35lb strength neo bar magnet using this method without overheating? Current supply isn't a problem for me, assume I have unlimited power for now, but I need to keep the added dimensions to a minimum so I don't know if i can pack that much magnetic strength into that small of an area or not.
If I increase the windings the magnetic field and wire resistance goes up and so does the heat generation limiting the current, if I decrease the windings the current goes up and the magnetic field is proportionally smaller requiring gobs of current. In either scenario I'm not sure whether I can achieve a "doubling" of magnetic strength without cooling methods. What do you think?

6. May 22, 2017

### marcusl

Physics Forums isn't a "we'll perform your design engineering for you for free" service. Look at the hysteresis curve and the formula for field from a solenoid. Figure out number of turns, current and heat dissipation and see if you can answer your question.