A MODEL FOR RESISTANCE OF A WIRE

PUMPTEST PIPE

A MODEL FOR RESISTANCE OF A WIRE.

In this diagram a pump is pumping water though a piece of “test pipe”. There is friction between the water and the pipe.This means that the pipe produces some RESISTANCE to the water flow.It also means that the flow of water makes the pipe warm.A longer test pipe would produce more resistance because there is more friction. This would slow down the flow of water.A wider test pipe would allow more water to flow through at the same time. It would have less resistance.

TEST WIRE

In this circuit a battery is driving current through a test wire.

As the electrons flow through the test wire they bump into the atoms in the wire.This slows down the flow of electrons and means that the wire produces some RESISTANCE to the flow of current.

It also means that the flow of current makes the wire warm.A longer wire would produce more resistance because there would be more atoms to bump into. This would make the current smaller.

A thicker wire would allow more electrons to flow through at the same time.It would have less resistance.

QUESTIONS:What part of an electric circuit is like the pump in the water ‘circuit’? _ _ _ _ _ _ _ _ _ _ _ _

What causes resistance in a water pipe? _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

What causes resistance in a wire? _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

If the test wire is made longer, what effect will this have on its resistance? _ _ _ _ _ _ _ _ _ _ _ _

If the test wire is made thicker what effect will this have on its resistance? _ _ _ _ _ _ _ _ _ _ _ _

The battery

In this diagram a pump is pumping water though a piece of “test pipe”. There is friction between the water and the pipe.This means that the pipe produces some RESISTANCE to the water flow.It also means that the flow of water makes the pipe warm.A longer test pipe would produce more resistance because there is more friction. This would slow down the flow of water.A wider test pipe would allow more water to flow through at the same time. It would have less resistance.

Friction between the water and the pipe

In this circuit a battery is driving current through a test wire.

As the electrons flow through the test wire they bump into the atoms in the wire.This slows down the flow of electrons and means that the wire produces some RESISTANCE to the flow of current.

It also means that the flow of current makes the wire warm.A longer wire would produce more resistance because there would be more atoms to bump into. This would make the current smaller.

A thicker wire would allow more electrons to flow through at the same time.It would have less resistance.

Electrons bumping into atoms in the wire

More resistance

Less resistance

If the length of the test wire is doubled,What effect will this have on its resistance?

Explain this. Use the idea of electrons bumping into atoms.

Resistance will be DOUBLED

There will be twice as many atoms for the electrons to bump into.

In a wire the atoms are vibrating. If the wire gets hotter the atoms vibrate more. The higher the temperature the more they vibrate.Does this make it easier or more difficult for the electrons to flow through the wire?

How does this affect the resistance of the wire?

More difficult

Increases the resistance .... Because it makes the current smaller.

The metal a wire is made from can affect its resistance. Write down 3 other factors that affect the resistance of a piece of wire.

Length of the wire

Thickness of the wire

Temperature of the wireWhich will also depend on the current flowing through it.