An Experiment To Investigate How The Length Of A Wire Affects The Resistance

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Abdulbasit Asif

An Experiment To Investigate How The Length Of A Wire Affects The Resistance

AIM:

To find out how the length of the wire affects the resistance.

BACKGROUND INFORMATION:

To make current flow through a conductor, there must be a potential difference (voltage) across it. Copper connecting wire is a good conductor and a current passes through it easily. However, a similar piece of nichrome wire is not so good and less current flows for the same PD. This is because the nichrome wire has more resistance than the copper wire. A basic definition of the term resistance is anything in the circuit that slows the flow down. So, resistance is the ability of an object to resist the flow of current.

Resistance is calculated using the equation:

RESISTANCE (Ω) = PD across conductor (V)

                          Current through conductor (I)

The unit for measuring resistance is the ohm. Its symbol is Ω. (The symbol Ω is the Greek letter omega).

The resistance equation was stated in ohms law. In a circuit there is always a balance between the voltage and resistance. The voltage is trying to push the current round the circuit and the resistance is opposing it. The relative sizes of the voltage and resistance decide how big the current will be. If you increase the voltage, then more current flow but if you increase the resistance, then less current will flow. With a lower resistance, a lower PD would be needed to give the same current. Even copper connecting wire has some resistance, however, it is normally so low that only a small PD is needed to make a current flow through it. In circuits, components called resistors are used to decrease or increase the flow of current. A resistor is a device with a particular value, used to produce a required potential difference. Resistors can have values from less than one ohm up to many millions of ohms. The most common type is the carbon resistor, made from compressed carbon of known resistivity.

The amount of resistance of a conductor depends on several factors:

  • Length - Doubling the length of a wire doubles its resistance.
  • Cross-sectional area - Halving the 'end on' area of a wire doubles its resistance. So a thin wire has more resistance than a thick one.
  • Material - A nichrome wire has more resistance than a copper wire of the same size.
  • Temperature - For metal conductors, resistance increases with temperature. For semiconductors, it decreases with temperature.

Resistance can cause a heating effect when a current flows through a resistance. This principle is used in heating elements, and also in the filaments of bulbs. This heating effect occurs because electrons collide with atoms as they pass through a conductor. The electrons lose energy. The atoms gain energy and vibrate faster. So the higher the resistance, the faster the atoms vibrate which means a higher temperature.

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The same theory of electrons colliding with atoms in a wire is used to explain the cause of resistance scientifically. In metal conductors, the current is carried by free moving electrons. Electric current will only travel if there are charges, which can move freely. Metals contain a sea of free moving electrons which are all negatively charged and which flow throughout a metal. This is what allows electric current to flow so well in all metals. The more energy the electrons have, the faster they will move as they have more energy. The higher the current, the more electrons will ...

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