How Does the Length of a Wire Affect Its Resistance?

How does the length of a wire affect its resistance?

Introduction:

This first report in Physics will show the investigation of how the length of a wire affects its resistance. For starters I will go through the main definitions, to get a better knowledge of what is going to happen. However I will plan it out first to show each step of how I started, and then go into detail about the results and what the investigation on a whole has showed me. I shall then conclude my findings and present them with tables and graphs saying what we discovered. There will also be an evaluation at the end explaining what went wrong and the experiment could have been improved.

This report on resistance should be easy to get through but the difficult area in my opinion will be to get the results accurately and displaying the different findings. I am working in a Group of 4 including myself and working in a team together should help us get an accurate output. I intend to work according to plan when the main investigation has started. This experiment has two sections which have to be carried out in order to get the correct results:

Preliminary work: Find out which wire is the best insulator?

Main experiment: How does the length of wire affect its resistance

Ohms Law:

Electric circuits are designed to transfer just sufficient energy to operate the components in the circuit. The potential difference across the components (and the current through them), are carefully controlled by the resistance in each part of the circuit:

The relationship between potential difference, current and resistance was discovered by a German physicist, George Ohm, in 1826. The relationship is known as Ohms Law and can be demonstrated experimentally as we are doing in this investigation. It states that the current through a metallic conductor is directly proportional to the potential difference across its ends, providing the temperature remains constant. However Ohms Law only applies providing the temperature of the conductor does not change. Resistance is measured in Ohms by resistors using the sign, Ω.

These are some of the standard symbols used in electricity calculations which we need, in order to carry out this experiment and receive proper results:

Current = I (A)

Potential difference = V (V)

Resistance = R (Ω)

Using these symbols, the relationship alongside can be written as:

R = V⁄ I

This equation can be easily changed to give values for the current (I) and the voltage (V):

I = V/R and V = I Ч R

Resistance:

The same relationship of Ohms Law is used to define resistance:

Resistance = Potential difference across the ends of a conductor

Current flowing through the conductor

Using the equation R= V/I, we can calculate the value of the potential difference, current or resistance if any two of the quantities are known. The higher the temperature of a conductor, the higher its resistance - due to the high values of potential difference and current. If a thin wire in a lamp tends to resist the movement of electrons in it, then we say that the wire has a certain resistance to the current. Which also proves that the greater the resistance, the more voltage that is needed to push a current through the wire. We will be measuring the resistance of wires in this experiment, to find out how the length affects it.

Before starting, we knew that the total resistance of a series circuit is equal to the sum of the separate resistance: R = R1 + R2

The resistance in parallel circuits has the same potential difference across each resistor. The combined resistance is less than either of the separate parallel resistances because the electrons find it easier to travel when they have more than one path to take. You can find the combined resistance using the equation below:

R= R1 Ч R2

R1 + R2

Voltage:

The reaction inside each cell (battery) releases the energy which electrons carry around the circuit and as the electrons pass through the cell, energy is transferred to them. The energy difference between the electrons leaving and the electrons entering the cell is called the potential difference of the cell and is measured in units called volts. The potential difference is often just referred to as the voltage. I have explained the formula for finding the voltage using the current and the resistance as shown on the previous page.

There is also a potential difference across every device in a circuit because energy is transferred to the devices by the current. This potential difference is measured using a voltmeter connected to the two points across where the difference is to be measured.

Some devices need more energy than others to work. Larger currents are needed to supply the extra energy. To provide a larger current, several cells may be connected in series (end - to - end).The potential difference in series circuits is different from parallel circuits. In series circuits the energy from the supply is shared between the devices in the circuit. This means that the potential difference across the supply is equal to the sum of the potential differences across all the devices in the circuit. The more devices which are added, the lower the potential difference across each one - so each one receives less energy assuming the supply does not change.

Current:

Electrical appliances only work when energy is transferred to them. The flow of electrons through the circuit is the electric current. All cells produce direct current. Direct current always flows in the same direction through a circuit - from the positive terminal to the negative terminal.

An ammeter is used to measure the current