Part IV: The Whole Ball of Facts: Technical Skills in .NET framework

Creator PDF417 in .NET framework Part IV: The Whole Ball of Facts: Technical Skills

Certain magnetic effects always accompany an electric current, and these effects follow definite laws In a wire, the magnetic lines of force (these lines are imaginary and used to explain magnetic effects) are perpendicular to the conductor and parallel to each other But, when you wrap a wire around a core and pass current through it, the wire forms a coil As the lines of force around the core take on a different shape, the field around each turn of wire links with the fields from the other turns of wire around it The combined influence of all the turns of wire produce a two-pole magnetic field very much like the magnetic field of a simple bar magnet one end of the coil is a north pole; the other end is a south pole The strength of the field depends on several factors Here are the main ones: Number of turns: If you increase the number of turns, you increase the field strength Closeness of the turns: The closer the turns, the stronger the field strength Amount of current flowing: If you increase current, you increase field strength Material in the core: Most coils are either air or soft iron Air coils are usually wrapped around a piece of cardboard; soft-iron coils are wrapped around a piece of iron Soft iron offers a better path for magnetic lines of force because its high permeability offers less reluctance to magnetic flux, resulting in more lines of force The more lines of force, the stronger the magnetic field Passing a suspended loop of conductive material (wire) through a magnetic field performs electromagnetic induction, which is the basic principle behind the electric generator Standing still, the conductor has no current flow But, when the conductor starts to rotate clockwise through the lines of force of the magnets, the lines of force induce free electrons to move through the wire

Magnetic effect: Magnetic force is produced when two simple magnets are brought together Each magnet has two poles: a north pole and a south pole When two like poles touch, the magnets repel each other When two unlike poles touch, the magnets attract and stick together A magnetic field surrounds magnets when magnetic force is working, which means that magnetic force extends beyond the magnets When a wire is introduced into the magnetic field, the wire becomes a conductor for the magnetic current Electricity flowing through a wire will repel a magnet If the wire is wrapped around an iron core and a current is sent through the wire, the iron becomes magnetized This effect is used to create energy through electromagnetic induction, the basic principle behind the electric generator Physiological effect: Current produces this effect when it passes through your bicep (or any of your muscles for that matter) and causes the muscle to contract This effect is used in medicine

Resistance interferes with the flow of current in a circuit But the flow of current is also impeded by two properties of alternating currents: Capacitive reactance (capacitance): The storage of energy that occurs in a nonconductor This property resists any change in voltage in a circuit Inductive reactance (inductance): The property that causes an electromotive force (another way of saying voltage) to be induced in a circuit

Capacitors store or hold a charge of electrons In an AC circuit, the capacitor is constantly charging and discharging (AC voltage goes positive and negative in each cycle) The rate of the charging and discharging acts as opposition to changing AC voltage as a resistive effect called capacitive reactance Inductors are coils of wire that make use of the properties of a magnetic field The property specifically desired in this instance is that of the current flowing through the wire With full current, the magnetic field is at maximum However, if you take away the current, the field doesn t disappear immediately It decays gradually, and the decay continues to push electrons in the path they were going But, in an AC circuit, the current constantly reverses The rate of changing current flow, and the resulting collapse and regeneration of the magnetic field in the coil, act as opposition to changing AC current a resistive effect called inductive reactance

These two types of reactance combine to impede the flow of current Impedance can be expressed as the ratio of electromotive force to the current: Impedance = Electromotive Force Current Electronics often require specific capacitive or inductive reactance to work Capacitors and inductors are devices used in circuits to provide the type of reactance needed Capacitors are rated in microfarads ( F) and inductors are rated in millihenries (mH)