explain why the direction of the current produced by an AC generator alternates.?

Answer 1

Picture two magnets with their north and south pole facing each other and seperated by a small distance. Within this seperation distance a coil of wire will be rotated.

Magnetic lines of force will travel between the North and south poles. The greatest concentration of magnetic lines are at the pole where a magnetic line exits the South pole and travels to the North pole.

Electricity is generated in a copper wire when the conductor is moved past a magnetic field in such a way as to cut across the magnetic lines of force (The conductor is at a right angle to the direction of magnetic lines of force). The polarity of current produced depends on two things the direction of relative motion of the wire across the lines of force AND the polarity or direction those lines of force are traveling.

So lets go back to that picture of the two seperated magnets
Between these magnets draw a circle which will represent the path of motion a conductor will take. The conductor in this case is oriented straight out of the paper

Starting at 12 O'clock the copper wire will begin moving in a clock wise circle . Note the direction of magnetic lines StoN and the wire will cut these moving Left to right. At this point the magnetic density is greatest so any voltage produce will be at its greatest potential. As you continue to mov the wire in a clock wise direction the number of magnetic lines that are cut decrease as the magnetic density decreases as its moves away from the pole. Also the relative motion changes so that at the three O'clock position the wire is moving in a direction parallel to the direction of the magnetic field. Here no line of force are being cut so no voltage is being generated. As the wire continues its rotation to six O'clock the magnetic density increases as it gets closer to teh south pole and the relative motion of teh wire and magnetic lines of for starts to increase.

Notice that at Six O'clock the wire is again at a position where it will be able to generate a maximum amount of voltage as it cuts across a dense magnetic field. BUT the relative direction of travel is NOW from Right to Left. Exacly Opposite of the 12 O'clock position. This reversal of direction actually happened at the 3 O'clock position.

Since the Magnetic field is still in the same direction South to North, we have only changed the direction of wire movement then the polarity of current produced is in the opposite direction.

Another way of see this reversal of current based on motion is to move a coil into the field of a horse shoe magnet. (You can monitor the voltage and polarity with a meter) As you hand pushes the coil in to the field you produce a current. Eventually you can only push the coil into the magnetic field so far. At which time you pull it out. You reverse direction of coil movment as you now pull it out of the field. The current produced is now traveling in the opposite direction.

Answer 2

Because the lines inside are cutting the Manetic field from positively to inversly.

Answer 3

only because rate of change in flux linkage. when the coil is in parallel with magnetic line of forces, linkage zero,when perpendicular, linkage max, .direction of current can be viewed by applying fleming"s left hand rule

Answer 4

The Magnetic Field Expands, then collapses, or goes in the reverse direction.

When the field expands, current goes one way.
When it collapses, or reverses, it goes the other way.

It is similar to blowing up a baloon, then sucking it out with a vaccuum cleaner.