I hope to find out how resistance of a wire is affected.

AS and A Level Science

Jason Berry 11H

INVESTIGATION TO SHOW THE EFFECTS OF THE RESISTANCE OF A WIRE

Aim: - I hope to find out how resistance of a wire is affected.

Prediction: - I predict that as the length of the wire increases the resistance will also increase.

Scientific Knowledge: -

A wire is a bundle of metal strips coated in plastic. The plastic can vary in colour and connect to different terminals

These are: -

Black = negative terminal
Red = positive terminal
Blue = neutral terminal
Green and yellow = earth terminal
Brown = live terminal

The material varies because it has free electrons, which are able to flow through the wire. The number of the electrons depends on the amount of electrons in the outer energy shell of the atoms, so if there are more or larger atoms then there must be more electrons available. If the material has a high number of atoms there will be a high number of electrons causing a lower resistance because of the increase in the number of electrons. Also if the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase. Resistance is measured in Ohm’s (Ω).

Ohm's Law

The law actually says that the resistance of a metal conductor is the same whatever the current - unless it’s getting hotter. However most people think of these equations when the law gets mentioned:

V = IR

V is Voltage in Volts, I is Current in Amps and R is resistance in Ohms.

This is a preview of the whole essay

Ohm's Law

V = IR

V is Voltage in Volts, I is Current in Amps and R is resistance in Ohms.

If the length of the wire is increased then the resistance will also increase as the electrons will have a longer distance to travel and so more collisions will occur. Due to this the length increase should be proportional to the resistance increase. If the wires width is increased the resistance will decrease. This is because of the
increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be less collisions.

Resistance is a force that acts against another it is also how hard it is to get current to flow through a component at a certain voltage. High resistance is hard for the current to flow. Low resistance is easy for the current to flow.

Current is the flow of electrons. There are two types of current: -

A.C. (Alternating Current) is where current changes direction (alternates) continuously. The number of complete cycles of reversal is called frequency. For mains electricity, the frequency is 50 cycles per second (50 Hertz). We can use a C.P.O (Comparative Phosphor Oscilloscope) to compare frequency and voltage.

D.C (Direct Current) is where the current always flows in the same direction. Cells and batteries supply a D.C. current.

Method

Set up the circuit as shown above WITH THE POWER SWITCHED OFF
First use a piece of wire of one meter in length then move the crocodile clips towards each other to the appropriate length; 90cm, 80cm 70cm, 60cm, 50cm, down to 10cm. This means you will have 10 results.
Turn the power on to 2 volts, then take a reading of the ammeter and the voltmeter
Before shortening wire to 90cm, allow two minutes for the wire to cool down because it will be very hot to touch and it would also be a unfair test.
Repeat the above until length is 10cm
Repeat the whole investigation for Reliability