Electric Forces and FieldsElectric Forces and FieldsHolt Physics: 17-1 Electric Charge Holt Physics: 17-1 Electric Charge

(Pages 628-633)(Pages 628-633)

2 Kinds of Electric Charge 2 Kinds of Electric Charge

Both were named by Ben FranklinBoth were named by Ben Franklin

1. Positive charge (+)1. Positive charge (+)

2. Negative Charge (-)2. Negative Charge (-)

Like charges repelLike charges repel

Opposite charges attractOpposite charges attract

Electric charge is conserved Electric charge is conserved

Electrons are transferred from one object to Electrons are transferred from one object to another when they come into contactanother when they come into contact

One object becomes negatively chargedOne object becomes negatively charged

One object becomes positively chargedOne object becomes positively charged

*** No charge is created or destroyed *** No charge is created or destroyed

The overall charge remains the sameThe overall charge remains the same

Electric charge is quantized Electric charge is quantized

Millikan’s oil droplet experimentMillikan’s oil droplet experiment Electric charge is measured in Coulombs (C) Electric charge is measured in Coulombs (C)

and is symbolized by “e”and is symbolized by “e” Quantized = occurs in discrete amountsQuantized = occurs in discrete amounts

++e , e , ++2e , 2e , ++3e , etc.3e , etc.

* Electrons have a charge of – e* Electrons have a charge of – e* Protons have a charge of +e* Protons have a charge of +e

* 1e = 1.60 x 10* 1e = 1.60 x 10-19-19 C C

Millikan’s oil droplet experimentMillikan’s oil droplet experiment

Transfer of electric charge Transfer of electric charge

The speed of transfer depends on materialThe speed of transfer depends on material

Conductor Conductor - Material in which electric charge - Material in which electric charge moves freelymoves freely

Most metals are good conductorsMost metals are good conductors

Insulators Insulators - Material in which electric charge - Material in which electric charge doesn’t move freelydoesn’t move freely

Glass, plastic, wood, and rubberGlass, plastic, wood, and rubber

Transfer of electric chargeTransfer of electric charge

Semiconductors Semiconductors - Materials with properties - Materials with properties between conductors and insulatorsbetween conductors and insulators

Specific atoms have been added to Specific atoms have been added to

alter the properties alter the properties

Superconductors Superconductors - Become perfect - Become perfect conductors at or below at certain conductors at or below at certain temperatures.temperatures.

Insulators and conductors can be Insulators and conductors can be charged by contact charged by contact

Charged by contact by rubbing 2 insulators Charged by contact by rubbing 2 insulators together and they attract each other together and they attract each other

Conductors charged by induction Conductors charged by induction

Process of charging a conductor by Process of charging a conductor by placing it near a charged object then placing it near a charged object then grounding the conductor. (Fig 17-4) grounding the conductor. (Fig 17-4)

Requires no contact between objectsRequires no contact between objects

Conductors charged by induction Conductors charged by induction

GroundingGrounding- when a conductor is connected to - when a conductor is connected to the earth by a wire or copper pipe.the earth by a wire or copper pipe.

Surface charge is Surface charge is polarizationpolarization

An insulator is placed near a charged object.An insulator is placed near a charged object.

Electrons in the insulator align themselves to Electrons in the insulator align themselves to

the charged object (all positive’s on one side,the charged object (all positive’s on one side,

all negative’s on the other side)all negative’s on the other side)

Conductors charged by inductionConductors charged by induction

Only charged on the Only charged on the surfacesurface

No net chargeNo net charge