Electrostatic charge transfer
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Electrostatic Charge Transfer. How do objects get charged?. Electrons can move Conductors electrons are “free” and can move throughout the material in good conductors, can move from atom to atom, and object to object Insulators

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Electrostatic Charge Transfer

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Electrostatic charge transfer

Electrostatic Charge Transfer


How do objects get charged

How do objects get charged?

  • Electrons can move

    • Conductors

      • electrons are “free” and can move throughout the material

      • in good conductors, can move from atom to atom, and object to object

    • Insulators

      • do not allow free movement of electrons throughout the material, or from the object to other things

  • Charges within objects are separated

    • Neutral atoms/objects

      • equal protons and electrons

    • Charged atoms/objects

      • more or less electrons than protons (depending on charge)


Law of conservation of electric charge

Law of Conservation of Electric Charge

net charges must equal zero


Within and object

Within and object:

  • If part of an object becomes charged, the other part of an object must become equally and oppositely charged.

    • Example: water molecules

Negative Pole

Positive Pole

Net overall charge: 0


Between 2 objects

Between 2 Objects:

  • If an object becomes charged from interacting with another, the other object must become equally, but oppositely, charged


4 ways to charge objects

4 Ways to Charge Objects

#1: Polarization

  • Surface charge (object remains neutral, overall)

  • Charges within object shift

    • in response to being near a charged object

    • Only while near the charged object.


Electrostatic charge transfer

Lightning


Electrostatic charge transfer

Lightning

  • Friction causes build-up of electrostatic charges in clouds

    • Bottom of cloud is usually negative

    • Negative buildup repels electrons in the ground, so surface becomes positive.

  • With enough buildup

    • Electrons are attracted to the earthand come down in a “streamer” of negative charges.

    • Positively charged air particles near the surface of the earth are repelled by the ground and form a “streamer” upwards.

  • When the streamers connect, a conductive path for an electron surge is formed – lightning occurs!

    • Air particles are so excited they emit light

    • Air is heated so intensely in creates sound waves (thunder)


Polarization demo

Polarization Demo

  • Watch the demo and answer the questions on your worksheet.


Experiment 1

Experiment #1

Charging by polarization.

  • Rub the round end of the balloon with the fur for a few seconds.

  • Hold the balloon against the wall and release it.

  • Observe what happens.


4 ways to charge objects1

4 Ways to Charge Objects

#2: Friction

  • Electrons transfer between objects by rubbing 2 neutral objects together (objects must have different affinities for electrons)


Electrostatic charge transfer

Charging by Friction


Experiment 2

Experiment #2

Charging by friction.

  • Rub one of the balloons on your hair for a few seconds.

  • Immediately hold it close to the other balloon.

  • Observe what happens.


Electrostatic charge transfer

4 Ways to Charge Objects

  • #3: Conduction:

    • - Requires one charged object, & one neutral object.

pith ball simulation


Electrostatic charge transfer

  • Step 1: Objects brought together to touch

  • Step 2: electrons transferred from charged to neutral (but polarized) object


Electrostatic charge transfer

  • Step 3: both objects now identically charged and repel one another.


Electrostatic charge transfer

The Electroscope

  • made of two thin metal leaves attached to a metal rod with a knob at the top.

    - when the device is not charged, the leaves hang straight down.

    - when an electric charge is present, the leaves repel each other, spreading apart.


Electrostatic charge transfer

Electroscope

electroscope simulations


4 ways to charge objects2

4 Ways to Charge Objects

  • #4: Induction:

  • Two neutral objects are in contact.

  • A third, charged object, is brought near the neutral objects to make them polarized.

  • The now polarized objects are separated making two oppositely charged objects.


Teacher demo

Teacher Demo

Draw a picture of what is happening to the charges in the aluminum cans.


Electrostatic charge transfer

Grounding

phet - travolta


K extensions

K Extensions


Electrostatic charge transfer

Conductors: metals, aqueous solutions of salts (i.e., ionic compounds dissolved in water), graphite, water, and the human body.

Insulators: plastics, styrofoam, paper, rubber, glass, and dry air.


Electrostatic charge transfer

How a Van de Graaff Generator Works:

Van de Graaff video


Sharing charge via conduction

Sharing Charge via Conduction

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  • A metal sphere (A) with a charge of +4 units is brought in contact with a metal sphere (B) with -2 units of charge, and the spheres are then separated. What is the charge on each sphere after separation?

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