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1. Oct 23, 2016

### Draff

I have learned the basic electronics and of course Volt ,amp, and ohm relation with the water pipe thing and Im just curious about some things that my prof(s) failed to answer

It says that what powers the circuit is actually current, does it mean that voltage and resistance variation is ok as long as the achieved current is the same? for example, if I have a simple bulb circuit, will lighting it with 5v the same as a 3v supply as long as I achieve a 15A output? (assuming the bulb can withstand 5v)

ground is shown in our circuit as connected to the negative of a DC circuit, when asked about it, my prof said that it varies if the circuit needs positive or negative supply, I have researched about it and they say that the ground is mostly a safety net of some sort, so that you wont shock yourself when things get out of hand. but in the circuit shown to us, the project (a traffic light simulation using LED) the ground seems unimportant as it is not connected to anything of the sorts. Is it safe to say that simple circuits need not have ground indications? except maybe showing if the circuit is positive or negative supply dependent?

in capacitor lecture, we were shown how the capacitor stores energy and how it releases it, my question is why is there a polarized capacitor and non polarized? under which situations should a electrolytic be used instead of ceramic? The site I read about talked about "what they're made of" but I dont see the point (over explanation of this somehow made me lose interest). and which is better?

in diode lecture, we learned about how diodes act as a "one way road" for the flow of the circuit, does the electrolytic capacitor not do the same?

Those are my questions

This part is just a note for everyone, as you may have noticed, I am slow in picking up lectures and I can't concentrate that well if things get too wordy so please keep it simple.

I have no computer at home so i rented in order to look up some of the questions only to realize that I spent half my time trying to understand 1 topic (the ground thing) by research, this is why I kinda bombarded this post with all my questions. I am sorry for this, please bare with me.

Thank you and have a nice day

2. Oct 23, 2016

### davenn

Hi
welcome to PF

no, not quite ...voltage is the first important part
if a device is stated at requiring 5V ( or whatever voltage) then that's what it needs to operate properly
The load ( your bulb) determines what current will flow due to its resistance. Just a note, bulbs are a little difficult as they change resistance
as they heat up, the resistance generally increases

Lets step back and look at a fixed resistive load.
take a 10V PSU and a 10 Ohm resistor, using Ohms Law I ( current) = V (voltage) / R Resistance)
therefore 10V / 10Ohms = 1 Amp
if you change the voltage upwards, then the current will increase and the resistor may burn out

You work out the current flowing for 20V and for 50V and post your working and answers

Dave

3. Oct 23, 2016

### Simon Bridge

Bear in mind that the water-pipe analogy is flawed - don't take it too much to heart.

No - the power dissipated by a component is the current through it multiplied by the voltage across it.
The brightness of a bulb depends on the power (and how it is made) ... for the same bulb, a higher power means a brighter light.
So if you keep the current the same, and change the voltage, you change the brightness of the light.

I think what they are trying to tell you is that it is the motion of the charges that makes stuff happen.

There is a distinction to be made between a circuit ground, where all voltages in the circuit are measured from, and a physical ground (which is a metal spike driven into the earth by your house) which acts as a safety feature.
A ground in a circuit just needs to have a reliable electric potential ... so you can call that V=0.
You only need the physical ground in cases where a fault could cause injury or property damage.

... it is due to the materials that were using in construction.
There are no hard and fast rules - you can build the capacitor out of sheet iron and air if you like ... these tend to be very big though.

That is because real materials are complicated and you are just starting out. You need to know that there are differences between commercial components that you can buy but you don't need to know why these differences exist just yet.

The things that determine what sort of comonent is used are the cost and size for a particular value, operating conditions, and tolerances.
If you open up something like a radio - you will see both ceramic and electrolytic caps in use - read their values and look at their sizes.
The choices and reasons can get quite complex but the biggest constraint is usually just economics.

... sort of, but there is a difference between "must be connected in a special way" and "acts like a one-way road".
If you try to use an electrolytic capactor connected the wrong way, it explodes.

4. Oct 23, 2016

### davenn

the use of the word "GROUND" can bring about all sorts of discussions
You will find many of them on PF if you do a search

But briefly, the use of the word "ground" needs to be defined for a given circuit

1) it may mean an actual physical connection to earth ground
2) it may be a connection to the metal chassis (case) of a device, with or without the type in point 1)
3) it may just refer to the battery or other PSU negative/0V rail

Dave

5. Oct 23, 2016

### davenn

no, diodes and capacitors are VERY different components and they don't operate the same way

Current will only flow one way through a diode UNLESS the PIV ( Peak Inverse Voltage) is reached
and this will breakdown the junction of the diode and destroy it

Current DOESNT flow through a capacitor. Current CAN flow in and out of either plate of the capacitor, but not between them

6. Oct 24, 2016

### Draff

does it mean that capacitor actually adds voltage to a part of the circuit? I mean, by what you said about current not flowing through it, with or without the capacitor, the current will be the same, but by adding it, the voltage that was supposed to flow normally, gets drawn to the direction of the capacitor?

7. Oct 24, 2016

### davenn

no, the capacitor will energise to the voltage in the circuit.
Capacitors have voltage ratings, if that rated voltage is exceeded then the capacitor will likely fail

on the other hand is a capacitor rated at say, 25V is placed across a PSU/battery of say 12V. Then the capacitor will only energise to that 12V

Dave

8. Oct 25, 2016

### Tom.G

Capacitors are two conductors (usually metal plates) physically separated by an insulator.

In non-polarized capacitors the conductors are often metal foil and the insulator may be paper, plastic film, or ceramic.

A common polarized capacitor is the Aluminium Electrolytic type. This uses Aluminium foil for one electrode and a conductive liquid chemical for the other electrode. The insulator is a thin insulating film that is formed on the surface of the Aluminium due to a reaction with the liquid. This whole combination acts as a capacitor. If a reverse voltage is applied, the insulating film is dissolved back into the liquid chemical. Without the insulating film, the Aluminium foil is in direct contact with the other electrode (the conductive liquid chemical) and a short circuit occurs. That's why @Simon Bridge mentioned in post #3 that "If you try to use an electrolytic capactor connected the wrong way, it explodes."

One advantage of an Aluminium Electrolytic is you can get a very high capacitance, and a high voltage rating, in a relatively small volume. This is because the insulating film on the Aluminium electrode is extremely thin. A disadvantage is they are not well suited to very low or very high temperatures. When very cold the conductive liquid freezes and doesn't conduct well, while at high temperatures the liquid tends to evaporate away.