# resistivity if a nichrome wire

Aim: Throughout this experiment I aim to find out the resistivity of a nichrome wire. To do this I will measure the resistance of the nichrome wire at different lengths and from this I will be able to work out the resistance using the equation:

Apparatus

Apparatus

Range

Accuracy

Purpose

Quantity

Nichrome wire

N/A

N/A

This is the wire that I will be calculating the resistivity for. It's the subject of the investigation.

Power pack

2V-12V

± 1 V

The power pack is used, as it's a supply of the initial voltage. It also creates a potential difference in order for the flow of electrons to occur (current to flow).

Crocodile clips

n/a

N/A

I will be using these to hold them to the nichrome wire and to the voltmeter. I will use two to connect the wire to the voltmeter and the other end attached to 0m on the wire. The other two will be used to move along the different length on the wire, from 0.100m to 1.00m.

4

Micro screw Gauge

0-25mm

± 0.01mm

This will help me measure the diameter of the nichrome wire. For this I can then be able to work out the cross sectional area of the wire by using the following equation: ?r2

Ruler stick

0m-1m

± 0.001m

This is to measure the different length of the nichrome wire.

Wires

N/A

N/A

They are connectors in the circuit. They connect the wire to the power supply, the ammeter and to the voltmeter.

4

Ammeter

0-10 A

± 0.01 A

This is used to measure the flow of electric current in a circuit.

Voltmeter

0-20 V

± 0.01 V

This instrument is used to measure the potential difference between two points in the circuit. Hence, the voltage across the wire.

Nails

N/A

N/A

I will use these to hold the nichrome wire to the meter stick.

2

Dependant and independent variables

Independent variable- The independent variable throughout this investigation will be the length of the nichrome wire. I will change the lengths to determine the voltage for each length. These results will therefore aid me in resolving what the resistance in the wire is.

Controlled variables

All there variables must stay constant in order to prevent them from affecting the dependant variables, and therefore creating anomalous results.

What to be kept constant

Why is it kept constant

How it's going to be kept constant.

Current supplied by the power pack.

Current is one of the factors which affect the resistance of the wire. It can affect the resistance of the wire. So if the current increases the resistance will also increase. This is because resistance is directly proportional to the current.

The power pack voltage will be kept constant, this will then therefore keep the current through the circuit constant.

Nichrome wire

Using different wires will affect my investigation; this is because different wires have different densities which determine its current flow.

I will ensure that I use the same wire throughout my experiment. By doing this I have abolished any chances of having wires of different resistively, cross sectional area or densities.

Equipment

Faults in the equipment due to them being old or broken might affect my results.

I will use the same equipments through my experiment to reduce any anomalous results.

Cross sectional area

The smaller the cross sectional area of the wire the less space that is available for the electrons to pass through, hence, smaller flow of current. However, with a thick wire the resistance is less as there is more space for the electrons to flow through.

I will control this as I will use the same wire throughout my experiment. This will ensure I have the same cross sectional area throughout

Method

. Measure the diameter of the wire using a micrometer screw gauge. It is taken in three places along the wire, and an average reading is taken. [D1 +D2 + D3 / 3].

2. Find the area of the nichrome wire using the formula of, ensuring that the radius is converted into meters.

3. The apparatus is then set. This is done by attaching the nichrome wire to the meter stick using a 2 iron nails. This will ensure that the wire is straight and has no kinks.

4. Attach the power pack to the voltmeter and the ammeter, this is done with the help of 4 pieces of wire and crocodile clips,

5. Set the volt meter to 10 cm.

6. Set the power pack to 2 volts, this will be kept constant.

7. Measure the voltage across the wire, by reading the voltmeter.

8. Repeat the experiment and this time change the voltmeter to 20cm.

9. Repeat this process up till 100cm.

0. Record the readings on the voltmeter and the ammeter (this will be constant) on a table.

A partial diagram of the practical set up.

(Fig 1)

Circuit diagram

(Fig 2)

Background knowledge

Resistance is a measure of a component's ability to an electric current through it. It is the resistance of a material of cubic shape of length of one meter

Good conductors of electricity have low resistance as current is able to pass through the component and poor conductors have high resistance, as there is no current flow.

To work this out we generally use this simple formula:

Resistance (Ohms) = Voltage (Volts)

Current (Amps)

There are many factors that affect the resistance of a wire these include:

The Temperature: When temperatures are increased, more energy is provided through heat. The electrons in the wire gain more kinetic energy causing them to vibrate more.

This means that the collision ...