Resistance

Planning and Prior Knowledge

Aim

To find out the effect that the length of a wire has on its resistance.

What is resistance?

A resistance is anything found in an electrical circuit that oppose (slows down) the flow of the electrons. Resistance also causes some loss of electrical energy when the electrical energy is turning to heat.

In a wire, the atoms (ions) of the metals slow down the electron

This diagram is shows that the electrons are finding it hard to reach the other end of the wire because they are colliding with ions, which causes friction and slows electrons down..

Measuring Resistance.

Resistance are measured in Ohms (О©).

The measurement of the resistance is followed by the Ohm’s law. The Ohm’s law was invented by a man named George Ohm in 1827. He invented it after an experiment

The Ohm’s law states:-

I= VÐ"*R

I= Current V=Voltage R=Resistance

Current is measured in Amps while Voltage (Potential Difference) is measured in Volts.

Electrical current are the movement of free electrons in the wire. Potential Different (Voltage) are the driving force that push the current .

For this investigation, we are trying to find the resistance. Therefore, we have to rearrange the formula given by George Ohm to find resistance.

I = V

R

I X R= V

R= V/I

By looking at the formula above for finding a resistance, mathematically, we can say that:-

i. The bigger the current, the smaller the resistance should be if the voltage stays at the same amount.

ii. The smaller the current, the bigger the resistance should be if the voltage stays at the same amount.

Factors that can affect my result.

There are four main factors that can affect my result. They are :-

i. Length of wire.

ii. Thickness of wire.

iii. Temperature of wire.

iv. Material of wire.

1. Length of wire

The length of a wire will affect the amount of resistance in the wire. Longer wires have more resistance than shorter wire. There are two main reasons for this. One is that the longer the wire, the bigger the length the electrons have to cover which will take more time. Due to this, the resistance increases. This is shown in the diagram below.

The second reason is that there are more ions in longer wire than in shorter wire, which will therefore slow down the electrons flowing.

As there are more ions in longer wires, the electrons flowing through the longer wire will be colliding with more ions as they gradually move to the other end of the wire. The number of collision happening in the wire has increased. Due this, friction is caused and the electrons slow down. As the electrons slow down the current decreases and the resistance therefore increases.

2. Thickness of wire:-

The thickness of a wire will affect the amount of resistance in the wire. Thicker wires have smaller the resistance

As the above diagrams show, the electrons are moving more freely in the thicker wire because there are more space in thicker wire. Therefore more electrons will be passing through the thicker wire. As more electrons are passing through the thicker wire, the current increases and when the current increase and voltage stays the same, the resistance reduces.

3. Temperature of wire

The temperature of a wire will affect the amount of resistance in the wire. The hotter the wire, the more the resistance in the wire.

The diagram is showing that the electrons are finding it hard passing through the hotter wire. The diagram is also showing that when the wire is hot, the ions that are in the wire are vibrating fast.

As the ions are vibrating fast because the temperature has increased, the electrons will be colliding into more ions which will make it harder for them to make to the other end of the wire- number of collision between the ions and the electrons increases in hotter wire. Therefore, the current reduces while the voltage stays the same and the resistance increases.

4. Material of wire.

The material the wire is made of will affect the amount of resistance in the wire. Different wires’ materials have different resistance. Wires’ that are made out of material that are good conductor of electricity have a smaller resistance than metals that are poor conductor of electricity.

Independent Variable

Independent variable is what I am going to change out of the four factors that affect resistance of a wire. The factor that I am going to change is the length of wire. The lengths of the wire that I am going to use for my investigations are :-

i. 10cm

ii. 20cm

iii. 30cm

iv. 40cm

v. 50cm

vi. 60cm

Dependent Variable

The dependent variable are the outcome