Resistance of a Wire Investigation

Resistance of a Wire Investigation

Resistance is to do with how easy it is for the electric current to

flow through a material, e.g. a piece of copper wire. Some materials

have virtually no resistance when they are cooled down to absolute

zero, they are called super conductors. Mercury will do this.

Materials like plastic, wood, polythene, ceramics and rubber have very

high resistances so that it is almost impossible for electric currents

to flow through them. These materials are called insulators. They may

not be perfect.

Materials like copper, silver, and gold have very low resistances. In

fact all metals will conduct electricity. They are called conductors.

Even so, they do have some resistance to the flow of electrons through

them. A perfect conductor is called a superconductor, it has zero

resistance.

Resistance is measured in Ohms.

Ohm's Law says that there is a relationship between these three

factors. So if you know two of the values you can easily work out the

third one.

V = I x R V

I = V / R

R = V / I I R

[IMAGE]The "V over I and R triangle" should help you to remember these

three equations. If you know the current and resistance and want to

calculate the voltage, you use the first equation. If you know the

voltage and resistance and want to calculate the current, you use the

second equation. Lastly, if you know the voltage and current and want

to calculate the resistance, you use the third equation.

The symbols used in the above equations represent:

o Current - Current is measured in amperes or amps for short. We use

the symbol "I" in the formula to represent current. (The reason for

using "I" rather than "C", is that "C" is already used for something

else.) The kinds of current flowing in our nerves and muscles are only

a few micro amps: the currents flowing in the mains might be as much

as 13 amps.

o Voltage - This is sometimes called potential difference or PD.