Alternating and Direct currents....help!?

Question

1. what are the difference between AC and DC and the manner in which each can be produced?
2. Why are baterries DC rather than AC?
3. How are generators and motors related?

Answer 1

1. AC stands for alternating current and DC stands for direct current.

From Wikipedia:
"An alternating current (AC) is an electrical current whose magnitude and direction vary cyclically, as opposed to direct current, whose direction remains constant. The usual waveform of an AC power circuit is a sine wave, as this results in the most efficient transmission of energy. However in certain applications different waveforms are used, such as triangular or square waves."

I always consider the sinusoidal voltage as
v(t)=Vpeak*sin(w*t)
Where w is the angular frequency. Sometimes a phase shift is included particularly when working with multi-phase currents like a household 240V in the US.

Direct current is V=Vpeak. Assumed to be a constant.

2. Batteries are DC because the electrical potential is created from a chemical reaction which has a constant voltage as long as there are sufficient concentrations of the chemicals around. In a dry cell, like a flashlight battery, the chemicals deplete and the battery become "weak" or "dead". In a wet cell like a car battery the chemicals are ionic solutions that can be rechaged by appying an external voltage source.

3. AC is most convienently created by converting kinetic energy to electrical energy by revolving wires in the presence of a magnetic field. As the wires rotate, they have an angular frequency w/r/t the magnetic field and a sinusoidal voltage waveform is created.
Motors are very similar in construction and with some care can also act as generators. This is an important component of the hybrid car. The car is accelerated using combustion of fossil fuel or stored energy from the batteries. When the "brakes" are applied, the decelleration is partially accomplished by regenerating electrical energy that again gets stored in the batteries. This is why they are so efficient in their use of fuel. Anyway, the motor is a set of windings in a magnetic field, by causing current to flow through the windings a force is created and the motor windings spin creating kinetic energy.

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Answer 2

Ac is alternating current DC is direct current.

AC oscillates backwards and forwards at a set number of times a second (50 Hz here in the UK) and the oscillations are simple harmonic so a sine wave displays it nicely.

DC goes in one direction, like a simple circuit, flowing out of one end of the circuit, round the circuit and back in the other.

Batteries are DC because an ionic chemical reaction is moving charge around and this happens in one direction in the cell.

Generators and motors are essentially the same thing just tweaked to make them more efficient in working in the direction they do, electricity => kinetic or vice versa. If you spin a motor it WILL generate electricity for you.

Answer 3

♣ if u r using DC trains will move from east to west only; if u r using AC they will move both directions;
♦ if u use a switch u can turn a battery into an AC source; don’t forget to toggle it with frequency 50Hz;
♥ by means of wiring! if you tug at one end a generator may tumble down; if you tug at another end a motor may tumble down; this is why the wiring is mounted on the posts! Lol!
♠ if serious I cannot add anything to answers of guys above;
a battery produces DC coz materials of anode and cathode are different;

Answer 4

DC machines can be classified as self-excited, separately excited, permanent magnet (PM), and brushless. Self-excited machines can be further classified as shunt, series, and compound. Compound machines can be further classified as cumulative and differential. Cumulative and differential machines can be further classified as long shunt and short shunt. As you can see, there are a variety of electrical configurations for a DC machine. For the purpose of this article, we will stick with the series- and shunt-wound DC motor. Please note that the interconnection of the field and armature (rotating winding) determine the machine's operating characteristics.
AC machines can be classified as induction, wound rotor, and synchronous. Induction motors can be further classified as 3-phase and single-phase. A 3-phase induction motor can be further classified as delta wound or wye wound. Single-phase motors can be further classified as split phase, capacitor start, capacitor start/capacitor run, shaded pole, repulsion start, and universal. As you can see, there are several varieties of AC motors. For the purpose of this article, we will stick with an overview of the induction motor.