CP9a Electric circuits

Identify the parts of an atom and

Describe the role of delocalised electrons

Distinguish between electron flow and conventional current

Atoms are largely empty space.

A tiny dense nucleus contains positively charged protons and neutral neutrons of about the same mass of 1 atomic unit

Negatively charged electrons with negligible mass surround the nucleus in cloud

The overall charge is neutral

Look at the diagram of a sodium atom. How many electrons and protons does it have?

Notice that the electrons are arranged in orbits called shells.

The inner shell can have up to 2 electrons in it and the next shells can have up to 8 electrons in them

How many electrons does the sodium atom have in it's outer shell?

Atoms in metals have very few (1 -3) electrons in the outer shell

They are weakly attracted, so can move between the atoms

They are called delocalised electrons

When a voltage is put across a conductor, the electrons begin to drift in one direction.

Current is now flowing in the circuit

Notice that the electrons are being pushed away from the negative terminal and attracted towards the positive terminal

This is called electron flow

Diagrams and all electricity rules show the current going from the positive to the negative terminal (the direction the scientists assumed it to be)

This is called 'conventional current'

To draw circuit diagrams we use standard components symbols that can be understand universally

Use the next slides, to see how many components you can identify.

Note cells convert chemical energy to electrical energy when connected to a circuit.

Batteries are actually two or more cells working together.