1.To recap what we can remember from Y11 about static electricity Book Reference : Pages 72-73 What…

1.1. To recap what we can To recap what we can remember from Y11 remember from Y11 about static electricityabout static electricity

Book Reference : Pages 72-73Book Reference : Pages 72-73

What can you What can you remember about remember about static electricity?static electricity?

What is it?What is it?

How is it made?How is it made?

What kinds of charges are there?What kinds of charges are there?

What part of the atom is involved?What part of the atom is involved?

What do What do likelike charges do? charges do?

What do What do unlikeunlike charges do? charges do?

What is it?What is it?Is an excess electrical charge (either positive Is an excess electrical charge (either positive or negative) which cannot move, either or negative) which cannot move, either because the material is an insulator or it is a because the material is an insulator or it is a conductor which is isolated from “Earth”. The conductor which is isolated from “Earth”. The charges charges cannot move cannot move and are therefore and are therefore staticstatic

How is it made?How is it made?Some materials allow electrons to be easily Some materials allow electrons to be easily removed from their atoms. For example when removed from their atoms. For example when a dry cloth rubs a plastic rod.a dry cloth rubs a plastic rod.

What part of the atom is involved?What part of the atom is involved?

Only the electrons which have a negative Only the electrons which have a negative charge are involved since they are the only charge are involved since they are the only particles which can be dislodgedparticles which can be dislodged

What kinds of charges are there?What kinds of charges are there?

Positive and negative. Things become Positive and negative. Things become positively charged when there are electrons positively charged when there are electrons missing or negatively charged when there is missing or negatively charged when there is an excess of electronsan excess of electrons

What do What do likelike charges do? charges do?

Repel (Push away/apart)Repel (Push away/apart)

What do What do unlikeunlike charges do? charges do?

Attract (Pull towards each other)Attract (Pull towards each other)

NB Same rules as magnetic polesNB Same rules as magnetic poles

Name some good electrical conductors Name some good electrical conductors and electrical insulators and electrical insulators [Jumper/Balloon [Jumper/Balloon Animation]Animation]

ConductorsConductorsMetals are good conductors & contain a “sea” Metals are good conductors & contain a “sea” of free electrons which are not bound to one of free electrons which are not bound to one particular atom & are free to move (conduct)particular atom & are free to move (conduct)

InsulatorsInsulatorsMost non-metals are insulators and do not Most non-metals are insulators and do not contain free electrons. The electrons are contain free electrons. The electrons are attached to individual atomsattached to individual atoms

Note Carbon, (graphite) is an exception & is a Note Carbon, (graphite) is an exception & is a non-metal which conducts electricity well non-metal which conducts electricity well

A gold leaf electroscope is a A gold leaf electroscope is a simple device which allows simple device which allows electrical charges to be electrical charges to be detecteddetected and and comparedcompared

[Electroscope Animation][Electroscope Animation]

Modern semiconductor integrated Modern semiconductor integrated circuits (silicon chips) are very circuits (silicon chips) are very sensitive to damage by static sensitive to damage by static electricity. Particularly CMOS electricity. Particularly CMOS (complimentary Metal Oxide (complimentary Metal Oxide Semiconductor) devicesSemiconductor) devices

AntistaticAntistatic Packaging and Packaging and handling precautions must be handling precautions must be taken to avoid damagetaken to avoid damage

When charged objects are brought together they When charged objects are brought together they exert an equal and opposite (non-contact) force exert an equal and opposite (non-contact) force on each other.on each other.

Consider a small object, which is free to move, has Consider a small object, which is free to move, has a positive charge and is brought near a fixed a positive charge and is brought near a fixed object which also has a positive charge then the object which also has a positive charge then the free object will be repelled and will movefree object will be repelled and will move

The path this free positive charge would take is The path this free positive charge would take is called the called the field line field line or or line of forceline of force

AA

BB CC

Experimentally we can plot the field lines for an Experimentally we can plot the field lines for an electric field in a similar manner to a magnetic electric field in a similar manner to a magnetic field. (We can use grains of semolina dusted on to field. (We can use grains of semolina dusted on to the surface of an oil film which has had a field set the surface of an oil film which has had a field set up across it).up across it).

Diagram ADiagram A shows the field created by oppositely shows the field created by oppositely charged objects. The field lines are concentrated charged objects. The field lines are concentrated near the objects and our free positive test object near the objects and our free positive test object would take a curved path to the negative chargewould take a curved path to the negative charge

Diagram BDiagram B shows a point object with a positive shows a point object with a positive charge near an oppositely charged plate. The field charge near an oppositely charged plate. The field lines are at right angles to the platelines are at right angles to the plate

Diagram CDiagram C shows a oppositely charged plates. shows a oppositely charged plates. There is a uniform between them shown by the There is a uniform between them shown by the parallel lines.parallel lines.

In keeping with gravitational and magnetic field In keeping with gravitational and magnetic field lines, the shape, density, (closer together shows a lines, the shape, density, (closer together shows a stronger field) and direction of the field is stronger field) and direction of the field is significant significant