Superconductors and Resistivity

What is a superconductor?

A material which has 0 resistance at or below its critical temperature.

What happens to the current when a material is superconducting?

It can flow indefinitely and repel a strong permanent magnet.

State and explain uses of superconductors.

Power cables that transmit electricity (0 resistance means no current is lost through the cables)

Strong electromagnets (high current repels a strong permanent magnet)

What is the resistance of electrical insulators like?

Very high.

What 4 things can effect the resistance of a material?

Length

Area

Temperature

Material

What happens to the resistance of a material as its length increases and why?

It increases as there are more collisions between electrons and metal ions.

What happens to the resistance of a material as its cross-sectional area increases and why?

It decreases as there are more gaps between ions for electrons to move through, so there are less collisions.

What happens to the resistance of a material as its temperature increases and why?

It increases, as the ions in the metal have more energy so vibrate more, causing more collisions with the electrons.

How can the material itself effect its resistance?

Some materials may have bigger ions or ions that are closer together.

Give the equation for resistance in terms of resistivity.

Resistance = Resistivity x Length / Area

Give the equation for resistivity.

Resistivity = Resistance x Area / Length

What are the units for resistivity?

Ohm metres

What instrument is used to measure the diameter of a wire?

A micrometer.

How do you use a micrometer?

1. Place the wire in the gap and tighten

2. Read the number of mm (to the nearest half mm)

3. Read to the nearest 0.01mm and add onto the first reading.