Question

A big chunk of my exam, anyone know anything :)​

Answer 1

Answer is mainly 2 parts where Part 1 is basic explanation of AC generator and origin of the law of induction in AC generator where Part 2 explains the reason behind Variation of current and EMF according to the rule..:

An AC Generator "Dynamo, Alternator" generates Alternating current according to the laws of Electromagnetic Induction in a straight wire

"Wire + Magnet + Motion= Electron flow" expressed in Faraday's law and Lenz's rule "EMF= -N ΔΦ/t"

In a straight wire moving perpendicular to a magnetic field, induction of Maximum EMF occurs in the wire according to the law of induction in straight wire derived from Faraday's rule and Lenz's law "EMF= -BLV Sinθ" Where "B" is Magnetic Flux density , "L" is length of wire ,"V" is the velocity which the wire moves by and "θ" is the angle between Magnetic Field and Straight wire and as usual the - is to apply to Lenz's rule

Switching back to the Alternator which is in form of a rectangular coil "4 straight wires"

We can conclude that the induced EMF rule must be 4BLV "Ignoring Lenz's rule since it's AC" but due to the presence of 2 sides parallel to Magnetic lines at the points of axle attachment so they do not induce current Sinθ = zero

EMF= 2BLV Sinθ . Since the coil rotates around itself "Rotatory motion" Thus, Velocity must be expressed in terms of Angular velocity where V "Linear Velocity" equals Omega "ω" (which is the angular velocity) multiplied by "r" (Radius of circle of motion)

EMF= 2BL (ωxr) Sinθ  . Since the coil rotates around its own axis then diameter circle of motion equals 2r which is basically the width of the coil "W" and radius = 1/2 W

EMF= BL*W ω Sinθ.. 1/2 cancels out the 2 and we have L*W which is Area of coil

EMF= BAωN Sinθ is the final form of the rule where N is added respecting the number of turns of coil where Dynamo produces maximum EMF at angle 90°,270° between magnetic lines and normal to coil

Reason of Alternation of current in the form of a Sinusoidal wave form "where EMF starts from zero rises to maximum emf descends to zero then descends again to -maximum emf then back to zero" is due to the coil's rotatory motion and changing of angle between magnetic field and normal to coil according to the above rule , For example Coil starts motion from zero position where the coil itself is Normal to magnetic field but the normal to coil is Parallel to the field so θ = zero thus no emf induced

After start of motion and rotation of coil using handle the angles start to change from 0° till 90° "1/4 cycle" Induced EMF increases from zero according to rule till reach maximum at 90° where Sin90 equals 1 , When continuing motion and according to sin graph value of EMF decrease as we proceed from angle 90° till 180° "another 1/4 cycle summing up to 1/2 cycle" where EMF reaches zero again at 180° since Sin180 equals 0, As we the rotation proceeds from angle 180° till 270° "another 1/4 cycle summing up to 3/4 cycle" EMF Increases till reaching Maximum BUT in opposite direction of motion since basically the - sign is a symbol of direction in physics but since the Graph is mathematical it is expressed as a decrease in EMF till reach -Max since Sin270 equals -1 which is opposite to max, Finally at the last quarter cycle from angle 270° till 360° EMF starts to decrease back to zero Physically but Mathematically seen as an increase since we were at -Max

So to sum it all up...AC current is due to Variation of Angle between Motion of coil and Magnetic lines causing the Variation of Current in tiny amounts of time with very high frequency

Answer 2

Answer:

Explanation:

As one side of the coil moves up through the magnetic field , a current is induced in one direction. As the rotation continues and that side of the coil moves down, the induced current reverses direction. This means that the generator produces a current that is constantly changing. This is alternating current or a.c..