Electricity
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Electricity. What is it?. Electricity is created inside the atom. Each substance is made up of atoms. Atoms contain a nucleus which is made up of protons and neutrons. . On the exterior of the nucleus are the electrons. These electrons move around in - PowerPoint PPT Presentation
Transcript of Electricity
What is it? Electricity is created inside the atom.
Each substance is made up of atoms.
Atoms contain a nucleus which ismade up of protons and neutrons.
electron
neutron
proton
On the exterior of the nucleus are the electrons.
These electrons move around in
an orbit around the nucleus.
Electrons can move from one atom to another. When one electron jumps from one to
another, another electron must move.
When electrons move quickly from one atom to another, the result is electricity!!
All object possess an electrical charge.
A charge can either be positive or negative depending on the quantity of
protrons and electrons.
Remember that all electrons possess a negative charge!
Charges??
Charges??Protons are in the nucleus and have a positive charge.
Atoms having more electronsthan protons will have _________ charge.
++
+-
- -
-
-
--
--
Atoms that possess more protons than electrons will have a ______ charge.
• Determine the charge on these two atoms.
10 electrons 2 electrons 5 protons 5 protons
Charges??++
+
++
-
-
-
-
+
Two objects with opposite charges will
Two objects with the same charges will
attract.
repel.
Opposite charges
will attract
Like charges will repel
Static Electricity Static electricity is a charge that
stays on the surface of an object.
The electrons move between the objects whenthey come in contact withone another.
Static electricity • Before rubbing the balloon in your hair, the two objects (your body and the balloon) are neutral (the quantity of protons are equal to the number of
electrons. )• After rubbing the balloon in your
hair, the electrons move from your hair to the balloon.
Remember!! PROTONS do not move!!!
• Your hair looses their electrons and the hair has a POSITIVE CHARGE.
Static electricity
Static electricity• Each strand is now
POSITIVE. Like charges push themselves apart and so that each strand now separates itself from one another.
Insulators and Conductors
- What are they?
Conductorrs• A conductor is a material that allows
electric currant to travel easily through it.
• Metals are good conductors.
• Examples: copper, gold, aluminum, brass, silver, stainless steel.
Conductors
Conductors allow electrical
currents to travel easily
because there is a lot of space for the
electrons to move.
Insulators •An insulator is a material that
does not allow electrical currants to travel easily through it.
•Examples: plastic, rubber, glass, wood.
Insulators Insulatorsblock the
electrons so they they have difficultytraveling through
the material.
Why is static electricity worse in winter?
Static electricity and winter•Cold air becomes much drier
in winter.•There are less molecules of
water in the air during winter.
•This aggravates the problem of static electricity.
•Dry air is an insulator, so it does not attract negative charges in our body.
•Normal air is a weak conductor, so a lot of our negative charges are attracted to the air during the other seasons.
•During winter, static electricity accumulates on our clothes and on painted and polished surfaces.
•Electrons wait until they find a source of protons, and then ZAP!!!
• Charging by friction
• Charging by contact
• Charging by induction
Let’s have a look!!
FLASH!!
The conductivity of solids
Conductors
Electrons can travel easily
high conductivity
Insulators
Very difficult for electrons to travel
high resistance
rubber
wood
pure water
metal
copper
SUPER CONDUCTORS SEMI INSOLATORSCONDUCTORS CONDUCTORS
salt water
silver
the Earth the human body
cotton
Electrostatic substances• Substances which become easily charged
• POSITIVE ~ Objects which loose their
electrons ~ glass, wool, cat hair, human hair,
silk
Electrostatic substances• NEGATIVE
~Objects which gain electrons ~ platinum, gold, rubber,
plastique
The principal of conservation of charge
• Electrons can neither be created nor destroyed.
• Electrons can move when two objects are in contact but the original number of electrons always stays constant.
•Charge it!- Read page 298 - 299 from
textbook.
Charging objects by FRICTION• When two objects enter in contact
many times (friction), the electrons leave one object and enter another.
A B
Charging objects by FRICTION
• Object A acquiers a charge
• Object B acquiers a charge
Ex: Balloon/comb in your hair
•The two objects were not already charged but now become charged during the process.
•The two objects possess opposite charges in the end, as the electrons left one object and went to the other.
List of electrostatic substances • Acetate• Glass• Wool• Cat hair, human hair• Calcium, magnesium, lead• Silk• Aluminum, zinc• Cotton• Wax• Ebony• Plastic• Carbon, copper, nickel• Rubber• Sulphur• Platinum, gold
Gives away it’s electrons easily (Positive charge)
Increasing tendancy to gain electrons
Electrons shared with great difficulty(negative charge)
Reflection questions
• A silk shirt and a pair of wool socks are placed in a dryer. What type of electrical charge will the silk shirt have after being rub with the wool socks? Explain your answer.
• What are the best types of brushes to use in winter: plastic or aluminum? Support your answers.
Lab demonstration –
what is happening?
Charging objects by CONDUCTION (contact)
• If an object which is already charged TOUCHES a conductor, the electrons will be transfered between the two objects.
Ex: your body and the door knob
Conduction ~ Negative charge
Negative charge
Conductor: carries a negative charge, which means there are more electrons in the conductor
than in the object.
When the conductor touches the object, the electrons will leave the conductor and enter the object.
In the end, the object will have a negative charge
Negative chargeNEUTRAL
Conduction ~ Positive charge
++NEUTRAL
Conductor: carries a positive charge, which means there are less electrons in the conductor
than the object.
When the conductor touches the object, the electrons will leave the
object and will enter the conductor .
In the end, the object will have a positive charge.
Conduction
BeforeDuring
After
ConductionAt the end of
conduction, the two objects have the same charge.
Why do we feel a shock when we walk across carpet?
When you walk acrossthe carpet, the electrons leavethe carpet and attach to your body. Now your body hasextra electrons. When you
touch a doorknob, the electronstransfer to the knob. ZAP!
You feel a discharge of electrons!!
Induction
• The two objects never touch, they are simply brought close together.
• Because there is never a direct connection, the electrons will not pass from one object to another, the electrons is simply displace within each object.
Induction
• OBJET A (already charged) approaches OBJET B ( a conducteur), but it never touches.
• Opposite charges will repel and the part of object B that is closest to object A will have the opposite charge.
• The other side of OBJET B will have the same as OBJET A
• An example: Lightening, dust on computer screen
Comb and water
• Take a charged comb and place it near a thin stream of water. What will happen?
+ =
Let’s have a look
What is it?Lightening is created due to strong
winds and the collision of water droplets and ice particles in the clouds that strip electrons from some particles and deposit them on others.
What causes lightening?
• Lightening is currents of electricity.
These collisions cause a current of electricity to be formed.
What causes lightening?
After a period of time, the clouds are filled with electrical charges.
Positives charges (protons) form at the top part of the clouds that are colder while the negative charges gather at the bottom of the cloud.
What causes lightening?The negative charges on the bottom of the
clouds repel electrons on the surface of Earth, levin the ground positiviely charged just below the cloud.
What causes lightening?The strong attraction between the negative cloud
and positive ground pull the electrons off atoms and molecules in the air.
What causes lightening? Once a chain of ions forms (usually
between highest objects), a gigantic discharge occurs between the cloud and the ground.
ZAP!!ZAP!!ZAP!!ZAP!!
ZAP!!ZAP!!
Interesting factsWhat is the temperature of
lightening? The temperature of the air
near a lightening bolt can reach as high as 33 000 degrees celcius, 3 times hotter than the surface of the sun!
Interesting factsHow can we tell the distance
between the lightening and the thunder?
If you count the seconds between a flash of lightning and a thunder clap, you can tell approximately how close the lightning is to you: each second representing about 300 metres.
About 10 people in Canada die as a result of being struck by lightning every year, and another 125 are injured. If you can hear thunder you are within striking distance, so head indoors.
Interesting factsWhat causes thunder?
• Thunder is caused by the lightening.
• When a lightening bolt leaves a cloud and travels to the earth, it opens a small hole called a canal. Thunder is the noise created when air suddenly expands from the heat of a lightning discharge.
Interesting facts• As the superheated air cools it
produces a partial vaccum surrounding the lightening’s path. This column vibrates like a drum and produces a tremendous crack. The sound echoes generating the rumble we call thunder.
• The reason we see lightening before we hear the thunder is that light travels faster than sound.
BOOM!!BOOM!!
Video!!
Video!!
Lightening rods
Photocopiers
Electrostatic precipitators
Smokestacks• Factories use static electricity to reduce
pollution coming from their smokestacks. They give the smoke an electric charge. When it passes by electrodes of the opposite charge, most of the smoke particles cling to the electrodes. This keeps the pollution from going out into the atmosphere.
Smoke stacks
How do fabric softeners work?
• If your socks cling to each other and snap at you when you try to pull them apart, that's static cling. Static is known to build-up in the dryer when fabric fibers, especially synthetics, rub together generating friction. As a result of the friction between fibers, electrons are transferred across surfaces resulting in a static charge.
• Fabric softeners works in the dryer where static happens. Softening ingredients are transferred from the dryer sheet to the surface of fabrics via heat and physical contact during the tumbling of the dryer. Lubricating fiber surfaces with fabric softener helps prevent the friction that leads to static charge. It gives fabrics similar surface electronic characteristics.
Why do birds not get electrocuted while sitting on
power lines?
• It isn't just insulation that keeps those pigeons safely perched on high-voltage wires. It's the nature of electricity at work. Electricity is always trying to reach the ground, and if an electrical conductor (like a wire or cable) provides a path, electricity will follow it. Electrical wires are always grounded. However, birds aren't grounded -- no part of them touches the ground -- so they don't act as conductors. The electricity seeks the path of least resistance-the wire and not through the birds.
If someone touches something that has no
grounding wire,their body is the best route
for the current and the person is
electrocuted.
Importance of grounding
Grounding
If someonetouches a wire that
is grounded, this wire
is the best routefor the electrical
current and not through the person. The
person will not beelectrocuted.
Video!!
Video!!
The end
