# Physics Course/Electromagnetism/ElectroMagnet/Coil of several Turns

## ElectroMagnet/Coil of several Turns

When a coil of several turns is connected with Electric source, Magnetic Field exist and has the same form as Magnetic Field of Natural Magnet. Current conducting Coil of several turns generates Electromagnetic Field of expanding Elliptical lines.

## Characteristics of Electromagnets

### Magnetic Poles

The polarities of the electric source form a Magnetic Pole. The Positive Terminal corresponds to North Pole and Negative Terminal corresponds to South Pole.

### Magnetic Field

Magnetic Field is made up from Expanding Magnetic Field Lines running from North Pole to South Pole. The Magnetic Field Strength is directly proportional to Current in the coil and the inductance of the coil and can be calculated by mathematical formula

B = L I

Where

I is Current measured in Ampere
L is Inductance measured in Henri

### Magnetic Field Force

The Magnetic Field Force is directly proportional to Magnetic Field Strength and the length of the Magnetic Field Line and can be calculated by mathematical formula

F = B l

### Magnetic Voltage Induction

Magnetic Voltage Induction on a Coil

${\displaystyle B=LI}$
${\displaystyle {\frac {dB}{dt}}=L{\frac {dI}{dt}}+I{\frac {dL}{dt}}=L{\frac {dI}{dt}}+0}$
${\displaystyle {\frac {dB}{dt}}=L{\frac {dI}{dt}}}$

Change of Magnetic Field strength is proportional to Inductance of the coil and change in Current flow through the coil

Magnetic Voltage Induction on a Coil's Turn

${\displaystyle \phi =NB}$
${\displaystyle {\frac {d\phi }{dt}}=N{\frac {dB}{dt}}+B{\frac {dN}{dt}}=N{\frac {d\phi }{dt}}+0}$
${\displaystyle {\frac {d\phi }{dt}}=N{\frac {d\phi }{dt}}}$

Change of Magnetic Flux strength is proportional to Inductance of the turns and change in Magnetic Flux through the coil