What would life be like without electricity? Copyright © 2010 Ryan P. Murphy.

Unit 6: ElectricitySection 1: Electric Charge and Force

• What would life be like without electricity?

Copyright © 2010 Ryan P. Murphy

• Much different than it is for most of us.

Electric Charge is a property of matter that creates electric and magnetic forces

and interactions. An object can have a negative charge, a positive charge, or no charge at all.

Let’s do a quick review of the atom to help us understand electricity…

• Electrons are negatively charged


• Electrons are negatively charged• Protons (nucleus) are positively charged


• Electrons are negatively charged• Protons (nucleus) are positively charged• Their charges are about equal


• Electrons are negatively charged• Protons (nucleus) are positively charged• Add Electrons - Atom becomes more

negatively charged (anion).


• Electrons are negatively charged• Protons (nucleus) are positively charged• Take away (strip) electrons - the atom

becomes more positively charged (cation).


• Annoying Tape.– Teacher gives each student 2 long pieces (10

centimeters each) strips of clear tape. • Make non-stick handles by folding a small amount

tape on itself.




tape on itself.

– Stick one piece of tape to table. – Stick the other piece of tape on that tape.– Quickly pull tape from table and then apart.– Observe what happens to the tape when it gets

close to each other and then eventually your arm.• Try and dispose of in trash barrel by shaking the tape

from your hand and not picking. Copyright © 2010 Ryan P. Murphy



tape on itself.

– Stick one piece of tape to table. – Stick the other piece of tape on that tape.– Quickly pull tape from table and then apart.– Observe what happens to the tape when it gets

close to each other and then eventually your arm.• Try and dispose of in trash can by shaking the tape

from your hand and not picking. Copyright © 2010 Ryan P. Murphy

• What happened?

• What happened?– When you removed the tape from the table you

gave it an electrical charge. When you peeled the tape apart from each other, one piece of tape gained more of a charge than the other.

• What happened?– When you removed the tape from the table you

gave it an electrical charge. When you peeled the tape apart from each other, one piece of tape gained more of a charge than the other.• Opposite charges attract (+) (-)



tape on itself.

– Stick both pieces of tape to table. – Quickly pull tape from table.– Observe what happens to the tape when it gets

close to each other and then eventually your arm.• Try and dispose of in trash barrel by shaking the tape

from your hand and not picking.




tape on itself.

– Stick both pieces of tape to table. – Quickly pull tape from table.– Observe what happens to the tape when it gets

close to each other and then eventually your arm.• Try and dispose of in trash can by shaking the tape

from your hand and not picking.


• What happened?

• What happened? – Each piece of tape gained a negative charge

when removed from the table. When they were brought close together they moved away from each other.

• What happened? – Each piece of tape gained a negative charge

when removed from the table. When they were brought close together they moved away from each other.• Like charges repel. (-) (-)

Opposite charges attract.


http://www.google.com/url?sa=i&rct=j&q=electric+force&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=https%3A%2F%2Fshare.ehs.uen.org%2Fnode%2F9044&ei=Ye3cVIX9Fsr3yQSCkICAAQ&bvm=bv.85761416,d.aWw&psig=AFQjCNEOnweE5Fo37GZ3jR3iajsK4fu7PQ&ust=1423851218201847

http://www.google.com/url?sa=i&rct=j&q=electric+force&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=https%3A%2F%2Fshare.ehs.uen.org%2Fnode%2F9044&ei=Ye3cVIX9Fsr3yQSCkICAAQ&bvm=bv.85761416,d.aWw&psig=AFQjCNEOnweE5Fo37GZ3jR3iajsK4fu7PQ&ust=1423851218201847

Opposite charges attract.


The Same forces repel.


• Which one is right and which is wrong?


• Which one is right and which is wrong?• Answer: They are both wrong.


• Which one is right and which is wrong?• Answer: Now they’re both right.


Conductors and InsulatorsConductor:• Material that allows electric

charges to move freely• Metals are good

conductors

Insulator:• Material that does

not allow electric charges to move freely

• Plastic is a good insulator

How do objects become charged?

• Charging by Induction:Electrons in the object move away or towards another charged object is placed close to it


• Charging by Contact:Electrons get passed from oneobject to the other when they touch


• Charging by friction:Electrons get passed from one object to the other when they rub against one another

• Activity- Bad Hair Day Demonstration.– Rub balloon all around your head.– Question: Why does this happen?


• Answer!– Electrons from your body move into the balloon.– This gives you a positive charge.– Your hair is also positive.– Like charges repel so hair tries to get away from

body.



body.


+

++? ?


body.


+

+? ?


body.


+

++

Charging by Friction is known as Static Electricity

Static Electricity: the imbalance of electric charges either in or on a material.

• Coulombs Law: Any two charged objects will create a force on each other. Opposite charges will produce an attractive force while similar charges will produce a repulsive force.

• Coulombs Law: Any two charged objects will create a force on each other. Opposite charges will produce an attractive force while similar charges will produce a repulsive force. – Coulombs Law: The greater the charges, the

greater the force. (Direct relationship) The greater the distance between them, the smaller the force. (Inverse relationship)

• Coulombs Law: Any two charged objects will create a force on each other. Opposite charges will produce an attractive force while similar charges will produce a repulsive force. – Coulombs Law: The greater the charges, the

greater the force. (Direct) The greater the distance between them, the smaller the force. (Inverse)

The electric force at the atomic level is responsible for most of the everyday forces that we observe, such as the force of a spring and the force of friction.

ELECTRIC FORCES AND FIELDS

ELECTRIC FORCES AND FIELDS

Electric force doesn’t require objects touch. An electric field always exists in the space around a charged particle. Any other charged particle in that field will experience an electric force.

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What would life be like without electricity? Copyright © 2010 Ryan P. Murphy.

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