ENB205 Electrical and Computer Engineering Week 1.dotx.docx

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Negareh Ghasemi

ENB205 Lecture Electrical and Computer Engineering 2 Magnetic Field Intensity (H): Magnetic Flux Density (B): (Wb/m ) (At/m) Proportional to move charge (I) Magnetic field is defined in terms of Magnetic Flux Density (B), which For a wire: at a distance r away loosely translates to how close the field lines are drawn. Magnetic field lines:  Always complete loops (no start or end like electric field For a coil: Of length l lines)  Always go from North to South poles  Never intersect each other. Permeability A measure of how easily something is magnetised. -7 Air is 0 = 4π*10 , everything else is measured relative to free space. Magnetic Flux Density The magnetic flux density (In a wire) created by the moving charge is proportional to the current in the wire. B= Magnetic Flux Density (T) I=Current in Wire μ0=Magnetic Permeability of free space -7 (4π*10 T/m) μr=Relative Magnetic Permeability r=Radius from centre of wire 1 Week 1 Tuesday, 27 August 2013 ENB205 Lecture Electrical and Computer Engineering Magnetic flux density (in a coil) can be increased by ‘coiling’ conductors create a solenoid. N=Number of turns I=Current L=Length Magnetic Flux Density (Loop) applicable only at the centre of the loop, and only for a single loop or wire. Flux Flux (Φ, wb Wei-ber) – If an imaginary surface is drawn, which the flux lines intersect perpendicular to, the total flux can be calculated. ∫ If the flux density inside this area is uniform, the total flux can be simplified to be: Faradays Law If the imaginary surface is bounded by a conductor, then as the flux changes in the area, a voltage is induced. Lenz’s Law The current induced in a closed loop due to changing magnetic flux, is such that is opposes the change in flux. If the flux is decreasing, current will flow in the direction which is constructive to the magnetic field. If the flux is increasing, current will flow in the direction which is destructive the magnetic field. 2 Week 1 Tuesday, 27 August 2013 ENB205 Lecture Electrical and Computer Engineering Flux Linkage For more than one loop, the induced voltage is summative such that (EMF= e = Electro magnetic field) The multiplication of turns and flux is called the ‘flux linkage’(λ) *Wb.t wei-ber-turn] Induced voltage may be expressed in flux linkage -> Absolute e =|e| = [V volts] Voltage induced on a moving conductor Voltage is also induced in a conductor as it moves through a magnetic field. B = Magnetic field density (measured in T – Teslas) V = Velocity of conductor L = Length of conductor in magnetic field α= angle between direction of field and direction of conductor movement Magnetic Dipoles The electron spin, creates a dipole, having both North and South poles. One pole cannot exist without the other. A net magnetic field is created when the un- paired electrons in a material are spinning in the same plane and direction. In a strong magn
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