Physics Unit 4 Electricity and Magnetism

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Physics Unit 4Electricity and Magnetism
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2 Forms of Electricity

1. Static a build up of charge on an object
2. Current a steady flow of electric charge
   through a conductor

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Static Electricity

• When objects are rubbed together, electrons can
  transfer from one object to another.
• ? the object that loses electrons takes on a
  positive charge.
• ? the object that gains electrons takes on a
  negative charge.

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Static Electricity

• Balloon is neutral.
• (Same of Protons as Electrons)

• Hair is neutral.
• (Same of Protons as Electrons)

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Static Electricity

• When rubbed together, the balloon accepts
  electrons from the hair.

• When rubbed together, the hair donates electrons
  to the balloon.

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Static Electricity

• Balloon becomes negatively charged.

• Hair becomes positively charged.

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Static Electricity

• Opposite charges attract. The hair is attracted
  to the balloon.

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Static Electricity

• Each hair takes on a positive charge. Hairs
  stand apart from each other because similar
  charges repel each other.

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Law of Attraction and Repulsion

• Opposite charges attract.
• Similar charges repel.

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Static Electricity

• If you scuff your feet on the carpet, electrons
  leave the carpet and are stored in your body.
• As long as you remain insulated from other
  objects, you simply walk around with excess
  negative charges. You have Potential Difference
  (Voltage)!
• When you touch another conductor, the charge
  transfers to that object. You feel a static
  electric shock.

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In addition to Friction, rubbing, objects can
also acquire a static charge by

• Induction When an object with a charge comes
  close to another object, it causes a temporary
  separation of charge in that object.

• Conduction When two objects make contact,
  electrons transfer between the two until their
  charges are equal.

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Conduction

• A negative wand comes
• near a neutral sphere.

• When they touch,
• electrons travel from the
• wand to the sphere.

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Neutral
The sphere becomes (-) charged by conduction.
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Induction

• A negative wand comes
• near a neutral sphere.

• The negative charge
• in the wand repels the
• electrons in the sphere.

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The side of the sphere near the wand becomes
charged by induction.


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When the wand is removed, the charge in the
sphere is removed.
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Static Electricity

• An excess of electrons, static electric charge,
  can be grounded by providing a path of conductors
  to the earth.
• Ex. Lightning rods on homes, grounding plugs on
  electrical cords

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Conductors and Insulators

• Conductors
• Allow a free flow of electrons.
• Ex. Metals
• (the wire inside an electrical cord)

• Insulators
• Slow or stop the flow of electrons.
• Ex. Rubber, Glass, Plastic
• (the rubber coating on the outside of an
  electrical cord)