# Solenoids and Force in Different Situations

1. Apr 1, 2014

### HannahSantos

I'm currently studying about Solenoids and Magnetic Fields. However, some questions are confusing me and I'm not really sure how to approach them. If I can get any input on them, I'd really appreciate it. ps, these questions aren't homework questions, they're questions that haven't been assigned since they're at a higher difficulty and I'm curious as to how they work out.

A solenoid is connected to a DC power supply such that the magnetic field is pointing out of the solenoid's on the end that is facing you.

a) a metal bar about 50% longer than the solenoid is inserted halfway into the solenoid. Does the metal bar experience any force from the solenoid? If so, in what direction?

b) i) With the metal bar removed, if you were to attempt to insert a bar magnet from the solenoid side where the magnetic field is going outward, North end first, what force, if any, would it experience?
ii) What if the bar magnet is inserted South end first?

2. Apr 4, 2014

In my opinion the bar-if it is a ferromagnetic metal made-will be attracted into the solenoid, it does not matter how will be introduced in the solenoid. The magnetic flow creates magnetic moments in the bar which represents a kind of magnet and will react with the flow-as in a lifting electromagnet.
The force is actually the lifting electromagnet force:
$$F=B^2*A:8\pi:9.81.10^5$$ =4.05/10^8*B^2*A kgf B [Wb/m^2] A[m^2] solenoid cross section area.
$$B=\mu_o.H$$
H=N*I/h [A/m]
$$\mu_o=4\pi:10^7$$ [H/m] N=solenoid no. of turns I[A] current h[m] solenoid length.

3. Apr 4, 2014