Physics Unit 4Electricity and Magnetism

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

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.

Static Electricity

Balloon is neutral.

(Same # of Protons as Electrons)

Hair is neutral.

(Same # of Protons as Electrons)

+-

+ -

+--

++

-

Static Electricity

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

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

Static Electricity

Balloon becomes negatively charged.

Hair becomes positively charged.

-

-

-

--

-

+ +

++

_ _

+

+

_

e-

Static Electricity

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

-

-

-

--

-

Static Electricity

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

Law of Attraction and Repulsion

• Opposite charges attract.

• Similar charges repel.

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.

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

charge by:

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

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

Conduction

A negative wand comes

near a neutral sphere.

When they touch,

electrons travel from the

wand to the sphere._

Neutral

_ _

_

The sphere becomes (-) charged by conduction.

Induction

A negative wand comes

near a neutral sphere.

The negative chargein the wand repels the

electrons in the sphere. _

_

__

++

The side of the spherenear the wand becomes+ charged by induction.

When the wand is

removed, the charge in

the sphere is removed.

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

Conductors and InsulatorsConductors:

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)