Conduction model and non-ohmic sensors Flashcards
What are insulators and what is an example of one which can conduct electricity under certain circumstances?
Insulators contain ions and electrons which are not mobile. In glass, sodium ions can move freely when glass is heated until it softens, so it can conduct electricity.
What are semi-conductors. How many atoms are ionised per set amount?
These contain one in every 10^12 atoms which are ionised. As semi-conductors are heated, electrons are liberated. This means that the conductivity of semi-conductors rises as free flowing charge carriers do.
What are thermistors?
Cheap semi-conductors. When heated, electrons are liberated and made mobile, so conductivity rises.
What are LDRs?
Semi-conductors. These are made from cadmium sulphide. As light intensity rises, electrons are freed, increasing conductivity.
When can thermistors or LDRs be used?
As sensors in potential divider circuits.
What are positive nuclei held by? What do the electrons have, and how is drift velocity created?
They are held by delocalised electrons in a strong metallic bond. Electrons have random velocity. When a voltage is applied, the electrons are attracted to the positive terminal, resulting in a drift velocity as they drift to the terminal like bees in the wind.
Describe how resistance works at room temperature and why it increases as temperature does.
Electrons and positive nuclei have kinetic energy. The nuclei vibrate as a result and stop the motion of electrons. As temperature rises, the vibrations increase, meaning more electrons are stopped. This increases resistance.
What is number density?
Number of electrons per m^3
What’s evidence that shows metals have large attractive forces?
High melting point and stiffness show that attractive forces in metals are large.
What does the conduction model suggest?
The conduction model suggests each atom donates one free electron.
