2330 practical assesment question

[Craigrg12]

hi guys,
just finishing off my level 2 2330 practical assesment couple of things got me kinda stumped know there really basic stuff just dont know how to answer them properly without sounding bit stupid really. the questions are :
why is the supply current reduced when a capacitor is in circuit?
and Why do choke voltage and lamp voltage when added together do not equal the supply voltage?
know there simple but just down know what to write down and explain them.
Any help would be great any pointers at all be brilliant
cheers thanks loads

 

[Spark123]

1) something to do with the power factor??
2) they are not in phase??

 

[thomo27]

hi guys,
just finishing off my level 2 2330 practical assesment couple of things got me kinda stumped know there really basic stuff just dont know how to answer them properly without sounding bit stupid really. the questions are :
why is the supply current reduced when a capacitor is in circuit?

Hi , Level 3 2330 student , my understanding is

A capacitor will pass alternating current but (apart from an initial surge) it will not pass d.c.
Capacitors are stores for electrical charges. Like tiny batteries they can cause a current to flow in a circuit. But they can only do this for a short time, they cannot deliver a sustained current. They can be charged up with energy from a battery, then return that energy back later. The capacitance of a capacitor is a measure of how much energy or charge it can hold.

So to summarise - the supply is reduced when the capacitor is fully charged

 

[davelx]

No, sorry, that's not it. A capacitor will pass alternating current, but the effective resistance (more properly called impedance) depends on the frequency.

There is actually no continuity of conductor from one side of a capacitor to the other. A useful analogy is to think of a water pipe with a rubber diaphragm across it. If you apply constant water pressure on one side, a small amount of water will initially flow from the other, and then stop - this is akin to charging the capacitor with DC.

If you apply alternating water pressure to one side - for example using a piston connected to a rotating wheel (this is analogous to an alternator), you will get continuous back and forth movement of the diaphragm and of the water on the other side. If you put a paddle wheel in the pipe on the other side it will rotate one way and then the other, which can be used to do work. You would see the diaphram moving first one way and then the other. In the same way, a capacitor passes AC by first charging in one direction and then discharging and charging in the other direction - all the time that the AC voltage is applied across it.

The question is impossible to answer unless you have a schematic of the circuit, as you have no idea where the capacitor is or what it is doing!

http://en.wikipedia.org/wiki/Reactance