An Investigation into the effect of thelength of a wire on its resistance.

Authors Avatar

Heather Oakley

An Investigation into the effect of the length of a wire on its resistance

Resistance is the ability of a substance to resist, or oppose, an electric current in a conductor. This resistance makes the electrons of a current give up some of their electrical energy. This energy is converted to heat, light and other energies. Resistance can be calculated by dividing the potential difference (p.d.) across its ends by the current passing through it:

Resistance (R) =   p.d. (V)  h

                    Current (I)

Resistance is measured in Ohms (Ω). One ohm is the resistance of a conductor through which a current of 1 amp passes when the p.d. between its ends is 1 volt.

When calculating the resistance, the p.d. is measured in parallel by a voltmeter and the current is measured in series using an ammeter.

There are several variables which affect the resistance of a wire.

Temperature of wire

If a wire is hot then resistance is increased because electrons find it hard to make a route through the vibrating particles. This diagram shows this theory:

The red line represents the current travelling through the wire

To stop the temperature of the wire from influencing my results, I am going to put a protective thermistor in the circuit to stop it from getting too hot.

Wire Thickness

Thicker wires have less resistance than ones with a smaller cross-sectional area because the current finds it harder to make a route through. This diagram shows this theory:

To stop the thickness of my wire affecting the experiment, I am going to use a micrometer to measure the diameter of the wire at various points along the wire to check that they are the same.

Wire material

Some materials let more current through than others. The degree to which materials conduct electricity is called resistivity. Conductors have a low resistivity; below 10-5 Ωm. Resistance can be calculated if the cross-sectional area, length and the resistivity of the wire is known:

R=     l                        The          in the equation stands for resistivity.

       A

To prevent this factor affecting my experiment, I am going to measure the resistance of the same wire, made from nichrome. The resistivity nichrome is 130 x 10-8. This is a high resistivity for a conductor, so the wire is expected to heat up quickly.

Join now!

The length of the wire will also have an effect on the resistance of the wire. The longer the wire, the more particles the current has to find a route through. This is the variable that I will be changing and investigating. Any change in the resistance of the wire in my experiment should be due to the change in length.

Method

Apparatus:                         

  • Power pack at 6V
  • Metre ruler                        
  • Connection leads
  • Protective thermistor
  • Nichrome wire
  • Crocodile clips
  • Ammeter
  • Voltmeter
  • Micrometer

Protective

thermistor

                 Nichrome wire

...

This is a preview of the whole essay