Transcript Physics_A2_Unit4_23_StaticElectricity01

Book Reference : Pages 72-73
1.
To recap what we can
remember from Y11
about static electricity
What can you
remember about
static electricity?
What is it?
How is it made?
What kinds of charges are there?
What part of the atom is involved?
What do like charges do?
What do unlike charges do?
What is it?
Is an excess electrical charge (either positive
or negative) which cannot move, either
because the material is an insulator or it is a
conductor which is isolated from “Earth”. The
charges cannot move and are therefore static
How is it made?
Some materials allow electrons to be easily
removed from their atoms. For example when
a dry cloth rubs a plastic rod.
What part of the atom is involved?
Only the electrons which have a negative
charge are involved since they are the only
particles which can be dislodged
What kinds of charges are there?
Positive and negative. Things become
positively charged when there are electrons
missing or negatively charged when there is
an excess of electrons
What do like charges do?
Repel (Push away/apart)
What do unlike charges do?
Attract (Pull towards each other)
NB Same rules as magnetic poles
Name some good electrical conductors and
electrical insulators [Jumper/Balloon Animation]
Conductors
Metals are good conductors & contain a “sea”
of free electrons which are not bound to one
particular atom & are free to move (conduct)
Insulators
Most non-metals are insulators and do not
contain free electrons. The electrons are
attached to individual atoms
Note Carbon, (graphite) is an exception & is a
non-metal which conducts electricity well
A gold leaf electroscope is a
simple device which allows
electrical charges to be
detected and compared
[Electroscope Animation]
Modern semiconductor integrated
circuits (silicon chips) are very
sensitive to damage by static
electricity. Particularly CMOS
(complimentary Metal Oxide
Semiconductor) devices
Antistatic Packaging and
handling precautions must be
taken to avoid damage
When charged objects are brought together they
exert an equal and opposite (non-contact) force
on each other.
Consider a small object, which is free to move, has
a positive charge and is brought near a fixed
object which also has a positive charge then the
free object will be repelled and will move
The path this free positive charge would take is
called the field line or line of force
A
B
C
Experimentally we can plot the field lines for an
electric field in a similar manner to a magnetic
field. (We can use grains of semolina dusted on to
the surface of an oil film which has had a field set
up across it).
Diagram A shows the field created by oppositely
charged objects. The field lines are concentrated
near the objects and our free positive test object
would take a curved path to the negative charge
Diagram B shows a point object with a positive
charge near an oppositely charged plate. The field
lines are at right angles to the plate
Diagram C shows a oppositely charged plates.
There is a uniform between them shown by the
parallel lines.
In keeping with gravitational and magnetic field
lines, the shape, density, (closer together shows a
stronger field) and direction of the field is
significant