Circuit loading

[Tommy volts]

Dear forum members:

I built a square wave generator which over heated when I ran it through an amplifier and speaker. I solved the problem I think, but am now trying to get a better understanding of loads, overloads, impedance etc. Please read the two quizes I prepared below. I have answered my own questions the best I could but need your checking. These questions form the very beginning of where I need to start understanding. This is not a joke (although it looks like one).

Sincerely: Tom


Given:

Circuit A is 10 light bulbs placed in parallel
Circuit B is 10 light bulbs placed in series
Same power source for each circuit
All bulbs are the same

True or False:

1. Each of the bulbs in Circuit B burn brighter than the bulbs in Circuit A. True

2. The current running through Circuit A is higher than the current in Circuit B True

3. If one of the bulbs in Circuit A is of higher resistance than the other 9 bulbs in Circuit A, then the higher resistance bulb draws less current and power than the others and burns dimmer than the others. True

4. If one of the bulbs in Circuit B is of higher resistance than the other 9 bulbs in Circuit B, then the higher resistance bulb draws the same current but more power than the others and will burn brighter. True


Given:

Standard 50 watt light bulb
Lincoln Arc welder (buzz box)
A 1000 watt hair dryer
A 1500 watt hair dryer

True or False:

1. While welding with the arcwelder, the arcwelder draws much more current and power than the burning light bulb. True

2. The only reason that the arc welder draws more current and power than the light bulb is because the arc welder has less internal impedance than the light bulb. True

3. The 1500 Watt hair dryer draws more current and power than the 1000 watt hair dryer. True.

4. The only reason that the 1500 Watt hair dryer draws more current and power than the 1000 watt hair dryer is because the 1500 Watt hair dryer has less internal impedance than the 1000 watt hair dryer. True

[Robert Reed]

First question (no.1) is false.

[Tommy volts]

Robert: Indeed. I mixed up the A's and B's on that one.

[ecerfoglio]

In your quizes you asume that your loads are connected to a "perfect" voltage source.

A "perfect" (or ideal) voltage source is one that outputs the same voltage while sourcig or sinking any current (from minus infinite to cero to infinite).

Of course, that is an ideal source, some "real" sources behave more or less like the ideal one, but most of them will lower their voltage when you load them. For example, when you use your welder or hair driers you might notice than your light bulbs get dimmer.

On the other end of the "real source scale" there are the current sources: They output the same current with any voltage you may load them.

In between, the source's behavior will deppend on the ratio of its internal impedance (or resistance) to the load´s own impedance.

"Perfect" voltage sources: Cero internal impedance (or resistance), cero voltage drop

"Real" voltage sources (120 VAC mains, car battery, etc): very little internal impedance (or resistance), very low voltage drop (you may notice it if you crank your engine with your lights on)

Signal sources (signal generators, antenas, video or RF lines, 50, 75 or 300 ohm): The internal impedance should be equal to the load´s, the "loaded" voltage is one half of the unloded voltage.

"Real" current sources: very high internal impedance

"Ideal" current sources: infinite internal impedance

<small>[ December 07, 2005, 11:52 AM: Message edited by: ecerfoglio ]</small>