1. Chapter 11 Electricity
Objectives: 1. Identify two forces that result from electric charges
2. Explain why objects attract and repel each other.
3. Communicate how positively charged object can be
used to determine the charge on another object.
4. Infer how electric charges behave in everyday
situations

2. “ + “ charge “ – “ charge “NO” charge
Review concerning Charge and Force
Recall that matter is made of atoms which contain
electrons, protons and neutrons.
“ + “ charge
PROTONS -
“ – “ charge
ELECTRONS
“NO” charge
NEUTRONS –

3. What do charged particles create?
The positive and negative electric charges in
objects can produce a force between the
objects. If charges are opposite, they will
cause objects to attract to each other. If
charges are alike the will cause objects to
repel or push away from each other.

4. FORCE OF ATTRACTION
“ + “
“ – “
Opposites attract

5. Like charges will repel each other
FORCE OF REPULSION
“-”
“-”
Like charges will repel
each other

6. ELECTRIC FIELD An electric field is a region surrounding
a charged object.
Strongest part of
field is closest to
the charged area
Weakest part of field
Is the area farthest away
from the charged object

7. Perhaps you have experienced this. When you drive
close to a power line you may get some “static” on a car
radio. What causes this?
Power line
Because there is an electric current flowing through
the power line there is an “electric field” around the
line. This electric field can cause “interference” on
your radio.

8. ELECTRICITY AND YOU
Your body uses electric signals to communicate with the brain.
If you touch something hot, the “-” charge inside the nerve cell
changes sending a signal along the nerve cell to the spinal cord,
to your hand, telling it to drop the object.

9. 11.2 STATIC ELECTRICITY
Objectives:
1. Identify three ways static charge can build up
2. Explain what causes lightning.
3. Compare electric conductors and insulators
4. Infer why lightning can be dangerous

10. Has this ever happened to you?

11. How does the person who “shocked” you become
“charged” with electricity?
First of all, you must understand that of the three
Particles that make up an atom, ONLY THE –e CAN
MOVE.
When the person who “shocked” you rubbed their
feet on the carpet electrons from the carpet were
moved to the person. This build up of electrons
“jumped” from their finger to your ear.
Static build-up is when electrons become overloaded
on an object. Static means stationary or not moving.

12. FRICTION In this example the person (object) became “charged” by
Can you think of other examples of causing
static build-up (charging) by friction?

13. CONDUCTION
Charging by conduction occurs when electrons are
transferred from one material to another by direct contact --
When the leaves of the electro-
scope become loaded with electrons
they repel and separate. -
-- -
------ -
electroscope
a device which detects an electrical
charge

14. INDUCTION - - - --- -- - - - - - --- - --- ----- -
Charging by induction occurs when charges are
rearranged without direct contact, the charged object
simple comes close to another object.
---
- ---
-----
What has become “charged”? -
The leaves of the electroscope
electroscope

15. LIGHTNING
HOW DOES IT HAPPEN ?

16. +_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+
When clouds are swirled around and blown together by
turbulence in the upper atmosphere, there is a great deal
of friction between the water molecules. This friction
causes electrons to be jarred loose and eventually there
is a build-up of electrons within an area of the cloud.
This is called “static build-up”. When this happens,
lightning can occur in several ways:

17. The most common form of lightning
+ _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _+ _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _
_ _ +_ _ _+ _ _ +
+ _ _ _ _ + _ _ _
_ _ + _ _ _ + _ _
_ _ + _ _ _ _
_ _ _ _ _ _ _ _ _ _ _ _
One end of the
cloud has more
+ charges.
The other end of the
cloud has more – charges.
The + - attraction between
the ends of the clouds causes
a “static discharge”(lightning)
resulting in a cloud which now
has evenly distributed + & -
charges.
What happens now?
Lightning within a single
cloud is called
“St. Elmo’s Fire”

18. + _ + _ When the negative end of one cloud comes close to
What will happen here?
_ _ _ + _
_ + _ _ _ +
+ _ _ _ _
_ _ _ + _
_ + _ _ _ +
+ _ _ _ _
+ + + _ +
+ _ + + _ _ _
+ + + _ +
+ _ + + _ _ _
A charged cloud
A second charged cloud
Where is the + - attraction?
When the negative end of one cloud comes close to
the positive end on another cloud you will see
lightning from one cloud to another.

19. + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ +_
How does one cloud “charge” another?
_ _ _ + _
_ + _ _ _ +
+ _ _ _ _
+ _ + _ + _ + _ + _ + _ + _ + _ + _ + _ +_
_ _ + _ _ _ + _ _ + _ _ _ +
+ + + _ +
+ _ + + _ _ _
+ _ _ + _ + + _ _
A charged cloud
A neutral cloud
When a charged object comes close to another object, the
second object becomes charged by __________________.
INDUCTION
What makes this happen?
Like charges repel so when the end with a large number of
electrons (-) comes close to the other cloud the electrons
in the neutral cloud are repelled to the other end of the
cloud causing it to have charged ends.

20. How does lightning strike things on the ground?
_ + _ _ _ + _ _ _ _
What happens?
+ + + _ + + _ + + +
A charged cloud
_ + + _ + +
A neutral
tree with
+ & - scattered
equally throughout
When the cloud gets close to
the tree the tree becomes charged
by induction. When the + / -
attraction becomes great enough
there is a static discharge of
electrons to the tree.
_ _ _ _ _ +

21. Why is it unsafe to seek shelter under a tree during a storm?
Lightning will try to find the
fastest way to the ground. The
people under the tree become
“charged” by induction just like
the tree does. As lightning
takes its path to the ground, it
will come out of the tree and to
the boys then to the ground.
_ + _ _ _ + _ _ _ _
+ + + _ + + _ + + +
A charged cloud
+ + + _ + +
+ + + _ ++ +
_ _ _ _ _ _

22. LIGHTNING
WILL
KILL YOU DEAD!
Don’t make someone cry.

23. CONDUCTORS
INSULATORS VS

24. CONDUCTORS - A material through which electric charges flow easily.
Examples include most metals such as gold, silver, copper,
aluminum and mercury. Non metals such as water and acid
are also good conductors.
NOTE: Pure water does not conduct electricity, it must
have some type of electrolyte or substance in it. Since the
water you use at home is not pure water, it is a good
conductor, it is wise to be careful when handling appliances
around wet areas.

25. INSULATORS: Materials through which electric charges
cannot move easily.
Examples include wood, ceramic, rubber, glass and plastic.
Note: you may have noticed that most wire to electrical
appliances are coated with rubber or plastic.
insulation
wire
In an insulator, the atoms are not arranged in a manner
which will allow the electrons to move freely. Therefore,
insulators are not capable of carrying electrical energy.

26. While drying, some clothes pick up a negative charge while
SCIENCE AND YOU
Do your clothes ever stick together when you take them of the dryer?
While drying, some clothes pick up a negative charge while
others keep a positive charge.
Using your knowledge about charges what happens?
Does your hair follow the comb or brush instead of lying flat?
Using your knowledge about charges, explain what you
think happens to your hair.