# Resistance in a Wire Coursework

Pages: 6 (1526 words) Published: March 19, 2012
Resistance in a Wire Coursework

In this investigation we are trying to look for resistance in a piece of wire, and how the length of a wire can increase or decrease the resistance. The things that affect the resistance in a wire are:

the length of the wire
a certain amount of wire
cross sectional area of the wire (thickness)
temperature
material

What things can affect the resistance in a wire?

The temperature can affect the resistance in a wire, because the more thermal energy a component has the more the atoms within it will vibrate and get in the path of the “free” electrons, so the higher the temperature, more resistance is being produced.

Material can affect the resistance due to the number of “free” electrons that are available to move or change in the atomic arrangement.

Cross-Sectional Area will affect the resistance as a larger cross-sectional area will provide more paths that the electrons can take enabling a low energy path to be taken and reducing the resistance, a small cross-sectional area has few paths so the resistance would be much higher.

And finally the Length could affect the resistance, the longer the component is the more atoms there will be for the electrons to be passed, and as each atom is surrounded by electrons they will repel the “free” electrons that form the current.

Relationship between Current, Voltage and Resistance

All materials are made up of atoms and all atoms contain protons, neutrons and electrons. Protons have a positive electrical charge, Neutrons have no electrical charge while and Electrons have a negative charge. Atoms are bound together by powerful forces of attraction existing between the atoms nucleus and the electrons in it’s outer shell. When these Protons, Neutrons and Electrons are together within an atom, they are happy and stable. However, if they are separated, they exert a potential of attraction called Potential Difference. If a circuit is created or conductor for the electrons to drift back to the Protons, the flow of electrons is called a Current. The electrons do not flow freely through the circuit; the restriction to this flow is called Resistance. Then all basic electrical or electronic circuit consists of three separate but very much related quantities, Voltage (v), Current (i) and Resistance (Ω). The relationship between Voltage, Current and Resistance forms the basis of Ohm's law which in a linear circuit states that if we increase the voltage, the current goes up and if we increase the resistance, the current goes down. A basic summary of the three units is given below.

Relationship between Voltage and Current in a circuit of constant resistance.

Quantity, Symbol, Unit of Measure and Abbreviation.

QuantitySymbolUnit of
MeasureAbbreviation
VoltageV or EVoltV
CurrentIAmpA
ResistanceROhmsΩ

To find Voltage (V)
[V = I x R] V (volts) = I (amps) x R (Ω)
To find Current (I)
[I = V ÷ R] I (amps) = V (volts) ÷ R (Ω)
To find Resistance (R)
[R = V ÷ I] R (Ω) = V (volts) ÷ I (amps)

How Resistance is measured
Resistance is measured in ohms. It can be calculated from the potential difference across a component and the current flowing through it. The total resistance of a series circuit is the sum of the resistances of the components in the circuit. Resistors, filament lamps and diodes produce different current-potential difference graphs. The resistance of thermostats depends on the temperature, while the resistance of light-dependent resistors (LDRs) depends on the light intensity.

Why do we get resistance?
An electric current flows when electrons move through a conductor. The moving electrons can collide with the atoms of the conductor. This makes it more difficult for the current to flow, and causes resistance. Electrons collide with atoms more often in a long wire than they do in a short one. A thin wire has fewer...