00:01
The magnetic field of a solenoid can also be determined with amperer's law.
00:08
That is, a solenoid is a stack of coils in which the length of the stack is much longer than the diameter of the cylinder shape, on which the coils have been wound.
00:24
Over on the left, i have shown an amper's rectangular loop that goes through the middle, of the stack and on the outside.
00:35
And the only place the magnetic field exists is along that central side of the rectangle on the inside of the stack.
00:46
So be projected onto the length of the stack is equal to mu -naut times the enclosed current, and that loop grabs onto n coils.
01:01
So ampher's law says that b times l is mu not times the number of coils times i.
01:09
So in the final expression for the magnetic field strength, it is going to depend on mu not, the constant, called the permeability of free space.
01:22
And that is always the same number unless you're filling it with iron or something like that.
01:33
And then little n stands for the number of turns per unit length.
01:39
And the current, of course, is the current that runs through the coils.
01:46
So here they usually give us the number of turns or coils in the stack...