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# Objectives: 1. Identify two forces that result from electric charges - PowerPoint PPT Presentation

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.

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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

Recall that matter is made of atoms which contain

electrons, protons and neutrons.

“ + “charge

PROTONS -

“ – “ charge

ELECTRONS

“NO”charge

NEUTRONS –

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.

“ + “

“ – “

Opposites attract

“-”

“-”

Like charges will repel

each other

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

close to a power line you may get some “static” on a car

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 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.

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

“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.

“charged” by

FRICTION

Can you think of other examples of causing

static build-up (charging) by friction?

Charging by conductionoccurs when electrons are

transferred from one material to another by direct contact

--

-- -- --

When the leaves of the electro-

they repel and separate.

• -

• -- -

• ------

-

-

electroscope

• a device which detects an electrical

• charge

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

HOW DOES IT HAPPEN ?

+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+_+

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:

+ _ + _ + _ + _ + _ + _ + _+ _ + _ + _ + _ + _ + _ + _+_ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _ + _

_ _+_ _ _+_ _+

+_ _ _ _+_ _ _

_ _+ _ _ _+_ _

_ _+ _ _ _ _

++++++++++++++++++++++++++++++++++++

_ _ _ _ _ __ _ __ _ _

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”

_ _ _ + _

_ + _ _ _ +

+ _ _ _

_

_ _ _ + _

_ + _ _ _ +

+ _ _ _

_

+ + + _ +

+ _ + + _

_ + + + +

+ _

+ + + _ +

+ _ + + _

_ + + + +

+ _

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.

_ _ _ + _

_ + _ _ _ +

+ _ _ _

_

+ _ + _ + _ + _ + _ + _ + _ + _ + _ + _ +_

_ _ + _ __ + _ _ +_ _ _ +

+ + + _ +

+ _ + + _

_ + + + +

+_ + + +_+_ + +

+ + + +_

+ _

+ _

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.

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.

_ __ __ +

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

+ + + _ + +

+ + + _ ++ +

____

+ _

+ _

+ _

WILL

Don’t make someone cry.

INSULATORS

VS

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.

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.

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.