electricity questions HELP

[Guest guest]

Hello everyone I'm new to the group and I hope we can help eachother

out, I'm a student at a technological University in El Salvador and

it's been a while since I graduated from high school and now I'm

trying to continue my studies.

I have home work about resistors, and the code of colors in the

resistors my question are:

what state of the matter resistors (resistences) belong to?

what does the code of colors represent in the resistors?

why the majority of resistors have carbon?

please help thanks Herbert Escobar aka Tito

[Guest guest]

>

> Hello everyone I'm new to the group and I hope we can help eachother

> out, I'm a student at a technological University in El Salvador and

> it's been a while since I graduated from high school and now I'm

> trying to continue my studies.

> I have home work about resistors, and the code of colors in the

> resistors my question are:

> what state of the matter resistors (resistences) belong to?

>

> what does the code of colors represent in the resistors?

>

> why the majority of resistors have carbon?

>

> please help thanks Herbert Escobar aka Tito

>

Tito,

Resistors essentially oppose the flow of electrical current in an

electrical circuit. Resistors are often carbon based but could be

wire wound with high resistance wire. Resistors come in various

resistor ratings from less than an ohm (unit of resistance) to many

millions of ohms referred to as megohms. Resistors are also rated as

to how much power they can safely dissipate before they burn up. The

values of resistances usually are marked on carbon resistors with

three color bands with a fourth band added to detote the tolerance

(precision) of the resistance value of that resistor. The tolerance

band is either silver or gold colored. The three resistance bands are

coded as follows:\

Black 0

Brown 1

Red 2

orange 3

yellow 4

green 5

blue 6

violet 7

grey 8

white 9

The first two bands are two significant digits of the R value and the

third band is a multiplier value. Therefore a resistor marked red,

orange, green, silver would have the following value:

2300000 ohms with a tolerane of 10% or 2.3 megohms.

The resistor code can be remembered in the following way (memorize

this): Bad Boys Rape Our Young Girls Behind Victory Garden Walls.

To understand how a resistor works in a circuit you must know ohms law

which is: E = IR, which means current (I) times Resistance ® equals

the voltage developed across the resistor. The power developed across

the resistor is EI = P which is Voltage x current = Power dissipated.

It is also E=I squared times R. It's usually best to derate the

resistor powerwise significantly. The tolerance is important in

precision circuits where you are trying to develop precision voltages.

Elemental circuit theory can show you how the resistor functions in

practice. In an electrical circuit you have a voltage source connected

to a resistor which is then connected back to the return of the

voltage source. This comprises the simplest electrical circuit.(of

course there are other components than resistors that could be in the

circuit but some sort of current limitation is needed). The voltage

generator develops the Voltage tension on the circuit which makes the

current flow toward the resistor and the resistor limits the current

flow back to the voltage source. The resistor in this simplest circuit

will develop a voltage across it equal to the voltage source. If the

Voltage source is capable of delivering the current without burning up

and the resistor has been selected with enough power dissipation

rating you will have a successful circuit.

[Guest guest]

Thanks MCNJNJ that was helpful man I really appreciate your Tutoring on this.

Tito

mcnjnj <olde_silas@...> wrote:

>

[Guest guest]

> >

>

The resistor in relationship to limiting the current from the battery

goes like this:

The voltage is E, the battery voltage, let's say 6 volts d.c. The

limiting resistor is what you would choose to limit the current to the

contacts. The other resistance is the resistance of your skin at the

particular point where you connect the electrodes. If you add the two

resistances (limiting R and Skin R) you will have the total resistance

in the circuit (ignoring the resistance of the wires which is

negligible in this case). Now, you don't know what the resistance of

your body is therefore you would have to hook up a current meter in

series with one of the wires (observing the correct polarity). Then

measure the current (start at a high current range and then lower the

current range on the meter to get a decent reading up scale). Once you

have the current for that particular set up and you know the voltage

then you can use Ohm's law, E=IR to solve for Rs, your skin

resistance, R=E/I. Now you can select the current that you want by

I=E/R where Rt will be the sum of the limiting resistance and your

skin resistance. Now, RL will be Rt-Rs which is the value of the

limiting resistor.

Actually, however, it's easier to get a potentiometer for the limiting

resistor and adjust it with the current meter in the circuit to the

proper amount of current.

Of course, if you move the electrodes you will need to use a different

limiting resistance value.