# solenoids

#### Roshela_kyoot

Joined Oct 6, 2005
8
Hi! roshela, im an ECE student, i have some questions...
1) what is the relationship between current in a wire and a magnetic field?
2.) how does the amount of current in the coil and the type of material affect the strength of an electromagnet?

---i really need some answers for my lab report...
THANKS!!!!

Joined Jan 19, 2004
220
the relationship between current in a wire and a magnetic field (in the case magnetic induction or magnetic flux density) is given by biot-sevart's law

B= ∫ (υ/4pi) (i*dl*sin θ )/(r*r)
where b is the magnetic induction
dl is a differntial length of conducting element
i is the current thru the differntial length of conductor
r is the distance of a point from the wire at which B is measured
(υ) is the permeability of the medium
direction of B is given by the Right hand screw Rule for cross product of vectors

in vector form the equation is given by

B = ∫ (υ/4pi)(i* dl*r)/(r*r*r)

where
dl is the vector representing the length dl in the direction of current i
r) is the radius vector directed from the differential element dl to the point at which B is measured

As you can see the value of B is indeed dependent on the value of i and the value of υ (which depends on the medium )..ie the value of B in iron (a ferromagnetic material) is much greater than the value of B in free space..thats why we use an iron core in electromagnets
the value of B in turn determines the strength of the electromagnet