What determines that a power source will produce AC or DC?
Ac is produced by rotating machinery in most cases, used because you can easily transform the voltage to different levels and trasnsmit over a long distance with little loss. DC is mostly produced by batteries and generally is useful as it does not go to zero with each cycle but has both constant polarity and voltage. For a resisive load the source is not important, but many loads will stop working with AC as the polarity reverses.
- If AC is more efficient than DC, why is DC used in automobiles?
In a car DC is stored by the battery in a chemical reaction, and this enables you to store power for later use, like to start the car later.
- On the oscilloscope, when the wave goes past zero, is electricity being produced?
Yes, power is the product of voltage and current, and with AC into a resistive load it is always going to be positive.
- In the analogy of the pipes and water it's mentioned that the power source doesn't produce the water/electricity. What does produce it?
A pump does, like in voltage the electrons do not produce voltage but this is generated by either an external force increasing the energy of the electrons or a chemical reaction doing the same.
- In the pipe analogy, it's stated that if the valve is closed there will be no flow but there will be still pressure. Would that pressure exceed the 12 volts because it has nowhere else to go and the pressure just keeps building at the valve?
No, the anology is not exact because the pump builds up to a pressure where the flow passes back through the pump for a centrifugal pump and for a piston pump till the force driving the pump is equal to the back pressure. This is analogous to the open circuit voltage as no current or water flows, this is the open circuit voltage or the closed pressure.
- The 110v doesn't produce enough amps to operate a kettle, so a greater voltage is needed. Why then in a car is a larger battery that will produce more amps but keeps the same voltage? Shouldn't a greater voltage be needed to produce more amps? How do two different sized batteries produce different amperages even though they have the same voltage? Sometimes even the same sized batteries produce different amps.
A kettle can be built to work on 110V, it just draws more current, and the max current is limited by the wiring. The relationship between current and voltage is resistance. A resistor can have a high value, and thus you need a high voltage to get a defined current to flow through it. A lower value resistor needs a lower voltage to get the same current. Voltage and current multiplied together gives power. You can have a low voltage and high current, or a high voltage and low current, but have the same power in a resistor. In a car battery you have the ability to deliver a lot of current, and the batteries may be rated for how much current they can deliver, this is generally given as cranking current, so that you can draw up to this current safely for a few seconds to start the car.
