# Regarding Solenoid and Magnets

nblu
Hello, I was doing some questions and I thought I was understanding solenoids and magnets in incorrect way..

The question was, what would you feel if you bring a magnet close to a solenoid. I've wrote 2 possibilities, first is that they will repel and the second is that the solenoid would shoot-out the magnet. I was thinking that if the coil on solenoid is loosely wound, the field lines within the coil are curved so it will repel.. but if it is tightly wound, the field becomes straighter and it will react more aggressively..

I've wrote down my ideas but wasn't really happy with what I've wrote..

Could anyone please direct me to a better answer? Thank you in advance.

## Answers and Replies

Homework Helper
The question was, what would you feel if you bring a magnet close to a solenoid. I've wrote 2 possibilities, first is that they will repel and the second is that the solenoid would shoot-out the magnet. I was thinking that if the coil on solenoid is loosely wound, the field lines within the coil are curved so it will repel.. but if it is tightly wound, the field becomes straighter and it will react more aggressively..

Your two possibilities are correct, but that would depend on whether you are bringing the North pole towards the north of the solenoid (remember how to find the direction of the magnetic field when a current is flowing?) and so forth.

and the magnetic field of a solenoid is given by $B=\mu n I$ where n is the no. of turns per unit length. If you wind the solenoid more tightly, n will increase and so will B and vice versa.

nblu
Your two possibilities are correct, but that would depend on whether you are bringing the North pole towards the north of the solenoid (remember how to find the direction of the magnetic field when a current is flowing?) and so forth.

and the magnetic field of a solenoid is given by $B=\mu n I$ where n is the no. of turns per unit length. If you wind the solenoid more tightly, n will increase and so will B and vice versa.

Thank you rockfreak, for your comment. I'll make sure that I mention the polarity as well when I explain. :)