Complete Summary Of The Magnetic Field - Class Science

Magnetic Field .
A magnetic field is the space around a magnet so that other magnets still experience a force . The space around a magnet can be described as an imaginary line as magnetic field lines that point out from the north pole of the magnet and enter the south pole of the magnet.

Magnetic Properties:
Similar poles, north pole to north pole, or south pole to south pole will repel each other. Two poles are not the same, the north pole and the south pole will attract each other.

Magnetic fields are not only generated by permanent magnets but also by electric currents. It was first discovered by Hans Christian Oersted in 1820; that around a wire carrying an electric current there is a magnetic field.

A. LONG CURRENT STRAIGHT WIRE

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To determine the direction of the magnetic field (B) use the right hand rule as shown below! 

• thumb shows direction of current (i)
• The other four fingers point to the direction of the magnetic field (B)

To determine the value of magnetic induction around a long straight wire carrying an electric current, the following equation can be used: \[B=\frac{\mu _{o}.i}{2\pi a}\] 

B. CIRCULAR WIRE CURRENT

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A live wire is then electrified, so the axis of the wire benefits a magnetic field whose direction is as shown.

The direction of the magnetic field is indicated by an arrow (Bp).
The magnitude of the magnetic induction around the wire (see picture):

• at the center of the wire ( point 0):\[B=\frac{\mu _{o}.i.N}{2 a}\]
• distance x from the center of the straight wire(point P):\[B=\frac{\mu _{o}.i.N}{2a}\sin ^{3}\theta\]

C. SOLENOIDE

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A solenoid is a coil of wire in the form of a long tube with very tight turns. 

A wire is shaped like a spiral, hereinafter referred to as a coil, when an electric current flows through it it will work like a bar magnet. This coil is called a solenoid.

• The magnitude of the magnetic field in the central axis of the solenoid (see figure - along the P axis) can be calculated: \begin{align*} B_p&=\frac{\mu _{o}.iN}{l}\Rightarrow n=\frac{N} {l}\\B_p&=\mu _{o}.in\end{align*}
• The magnitude of the magnetic field at the tip of the solenoid (see figure - along the U axis) can be calculated: \begin{align*} B_u&=\frac{\mu _{o}.iN}{2l}\Rightarrow n=\frac{N}{ l}\\B_u&=\frac{1}{2}\mu _{o}.in\\B_u&=\frac{1}{2}B_p\end{align*}

with:

• B = magnetic field on solenoid in tesla ( T )
• $\mu _{o}$ = permeability of vacuum = $4\pi .10^{-7}$ Wb/amp.m.
• I = electric current in amperes (A)
• N = number of turns in solenoid
• l = length of solenoid in meters (m)

D. TOROIDA

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Toroid; The image on the right shows a toroid which can be described as a solenoid bent into the shape of a donut.

• The magnetic field B at the core of a toroid is given by:\[B=\frac{\mu _{o}.i.N}{2\pi a}\]
• Magnetic field B inside the toroid (point P): Zero
• Magnetic field B outside the toroid : zero