# Group 4 project

Electricity:

Electrostatics:

• Not moving charges.
• Material like amber, when rubbed, can move small objects
• The technical term is that the ‘balloon’ or likewise, is electrically charged
• There are two types of charge:
• positive
• & negative
• if we are looking at atoms, protons are positively charged and electrons are negatively charged
• An object that is not charged is referred to as neutral.
• A neutron has no charges

• In most situations we don’t look at atoms, we look at whole objects
• If an object has more electrons that usual it will be negatively charged.
• If it has less electrons, it will be positively charged.
• In most cases we can use friction and rub electrons from one object to another to charge it.
• It is important to note:
• electrons do the moving, NOT protons
• the charge doesn’t last long due to interactions with air
• it is not restricted to solids

• electrostatic precipitation – in chimneys.  Smoke and dust are ionized and stick to the metal plates in a chimney
• the basic technique of charging small particles is how photocopiers work

Charging an object

• can be easy or hard depending on the conductivity of the object.
• In a conductor electrons can move very easily. E.g. metals have delocalized electrons that move easily.
• In an insulator electrons are NOT free.
• Things you can CHARGE are insulators.

Charging by induction ← induced charge

The charges are induced.

One is negative one is neutral.

This then induces a positive charge on one end of the neutral.

Attraction occurs.

Like charges repel, opposite charges attract

The gold leaf electroscope:

Colomb’s Law

The force is dependant on:

• Size of each charge
• Square of the distance between them

where ε is the “permittivity of free space.”

Where: k = “coulomb constant”

= 9 x 109 Nm2C-2

q1 + q2 are charges measured in coulomb’s.

Electric Fields:

• We often draw field lines to visualize forces.
• You draw a field by pretending to put a ...