Electrostatics and Current Electricity

GCSE Physics Double Award notes

1. Electricity 1
Electrostatics
and
Current Electricity

2. Aim of the lesson
Static charge
3.6.26 recall that insulating materials can be
charged by friction and explain this in terms of
transfer of charge.
3.6.27 identify that positively charged objects
have a deficiency of electrons and negatively
charged objects have a surplus of electrons.
3.6.28 describe the dangers and use of
electrostatic charge generated in everyday
contexts.

3. Text Book Reference
Physics CCEA pg 109-113
Electrostaticsis the study of charges at
rest

5. Sir Ben Frank
Fly that kite…

6. Electrostatics
The organisation of the parts of an atom
has electronsorbiting a large central
nucleus of nucleons (neutrons and
protons)
neutral atom positive ion negative ion
These models are NOT to scale

7. If there is an unbalanced number of
protons (positive carriers) compared to
electrons (negative carriers) then the ion is
called a charged particle
3 electrons, 3 protons-
no charge
2 electrons, 3 protons-
positive charge
(deficiency of
electrons)
4 electrons, 3 protons-
negative charge
(surplus of electrons)
-
-- -
-
- -
--
+
++ ++ ++
+ +

9. Charging by friction
The wool and polythene
are each ‘uncharged’.
What does this mean?
In this diagram:

10. Charging by friction
The wool is ‘uncharged’,
because…
…it has equalamounts
of positive and negative
charge.
Equal numbers of
+and −
On the wool
+ −
+
+ −
−+ −
−
+ +
− −
+
+
−
+
−
−
+
On the polythene

11. Charging by friction
Equal numbers of +
and −on the wool:
(Count them!)
7+7−
Equal numbers of +
and −on the polythene:
(Count them!)
3+3−
+ −
+
+ −
−+ −
−
+ +
− −
+
+
−
+
−
−
+

12. Charging by friction
If you rub the wool on
the polythene, some
electrons(−) move from
the wool to the polythene.
There are now more +
than −on the wool:
(Count them!)
+ −
+
+
−+
−
+ +
−
+
+ −
−
+−
−
− −
+
So now the wool is charged positively,
with a surplus of 3 +

13. Charging by friction
What has happened to the
polythene?
There are now more −
than +on the polythene:
(Count them!)
+ −
+
+
−+
−
+ +
−
+
+ −
−
+−
−
− −
+
So now the polythene is
charged negatively,
with a surplus of 3 −

14. Charging by friction
Bothobjects are
equallycharged,
with oppositecharges
because electrons −
(only) have moved
from the wool to the
polythene.
This is summed up
in the diagram-

15. The overall effect of these charged particles
produces a force
If the electrical charge is ‘held’ on the
surface of a material it is referred to as
static electricity.
This type of charge cannot movethrough
out the material (an insulator)
Charged objects exert an electrical force-
similar charges repeleach other and
opposite charges attract.

16. The electrical static charge can be produced
in two ways-by frictionand byinduction.
The attractive forceswhich keep the
electrons (negative) close to the nucleus
(positive) can be easily overcome.
The electrons have relatively low mass
compared to the nucleons and therefore it is
only ever the electrons which can be
transferredthroughout a material or from
one material to another.

17. Everyday examples of
electrostatic
Lightning-the bottom of a cloud can be
charged by friction of other air particles to
produce a large negative
electrostatic charge.
This can be discharged
on the positively charged
upper surface of another
cloud or the positively
charged ground.
Page 111 and 112
+++++
++++
-------

18. Electrically conductive truck tyres-
These tyres drain any charge built up by
passing air particles. This safety feature
stops any sparks occurring which might
prove explosive for any trucks carrying
large amounts of fuel.

19. Air Purification-Industries release a huge
amount of air pollutants into the atmosphere.
25000 V 0 V
Electrons
repelled
Positives fixed
Dust
particle
Some of the fine
dust can be
eliminated by
passing the
exhaust through
charged
electrostatic plates
which attract the
charged smoke
particles
+
+
+
+
+
+
+
+

20. Aims of the lesson
Charge flow
3.6.29 understand that an electric current is a
flow of electrons and that it is in the opposite
direction to that of a conventional current.
3.6.30 recall that charge is measured in
coulombs.
3.6.31 recall and use the quantitative
relationship between current, charge and
time.

21. Factoids
The charge on one Electron is
1.60 x 10
-19
C
0.000 000 000 000 000 000 160 Coulombs
There are roughly 1 x 10
21
electrons in a
1 m length of metal wire
~1 000 000 000 000 000 000 000 electrons

22. Current flow within a
circuit
The flow of electricity in a circuit is due to the
charge, Q,moving within the material (copper
wires).
The speed of the flow is known as the
current(symbol I)
This is similar to the flow of water in a river being
called a current-when it flows fast there is a
strong current.

23. Current Definition
Electrical Current is the rate of flow of
charge past a given point in a circuit
How fast or the
time it takes…
The number of
charged particles
Current= Charge / Time
I = Q/ t
Amps= Coulombs / Seconds
Symbol
Equation
Units
Equation

24. Electrical Current
Reference Page 114

25. Circuit Diagrams
Page 115
3.6.34 describe and record
diagrammatically simple electric circuits.
-Draw a circuit diagram of the circuit
which is set up by Mr McClelland
-A simpler way of representing a circuit
visually is using the set of electrical
circuitsymbolsto represent each
component.(make sure you know them!)

26. Draw the circuit
SwitchVoltmeter in
parallel over
a bulb
Two Bulbs
in parallel

27. A
V

28. Conventional Flow v Electron Flow
Page 114-Electrical
current is
conventionallyknown
as flowing from the
positive terminalto
the negative terminal.
However, we refer to
the electrons as
flowing from the
negative to the
positivedue to the
attractionthat the
negative charge has
to the positive
terminal.

29. Conductors-The electrons are free to
move within these materials, very little
energy is required to free the electrons
from their atoms. (Metals, carbon)
Insulators-Charge cannot move through
these materials as they have very few
free electrons. (Plastics, ceramics,
rubber)
The Movement of
Electrons

30. Experiment-Electrical
Current
Set up the following circuits and find the
electrical current flowing at each point
indicated.
Series
Parallel
+

31. Results
Table
Point on the circuitCurrent (A)
0.25
0.25
0.5
0.25
0.25

32. Conclusion
The ammetermeasures the current
flowing in the circuitas the electrons
pass through it.
For a series circuitthe electrical current
will be the same at every point
For a parallel circuitthe current entering
the parallel section will be equal to the
sum of thecurrent of the branches of the
parallel section (currentsplits)

33. Extra Syllabus Reference-
3.6.36 recall that in a series circuit the
current is the same everywhere.
3.6.38 recall that in a parallel circuit the
sum of the currentsin the branches is
equal to the current enteringthe parallel
section.

35. So eh, what’s the current?
Series- Parallel-
+
Current the same
everywhere!!
Current into the junction is
equal to the current out

36. Examples of current in a
circuit
What is the reading on each of the
following ammeters-
3A
A
1
A
2
A
3

37. Bad Parents…