12
Forces and Fields Forces and Fields Electrostatics Lesson 3

Forces and Fields

Embed Size (px)

DESCRIPTION

Forces and Fields. Electrostatics Lesson 3. Electrostatic Series. Increasing tendency to hold on to electrons. Increasing tendency to lose electrons. Whichever material is closer to the top holds electrons more tightly so will gain a negative charge. - PowerPoint PPT Presentation

Citation preview

Page 1: Forces and Fields

Forces and FieldsForces and FieldsElectrostatics Lesson 3

Page 2: Forces and Fields

Electrostatic SeriesElectrostatic SeriesSulphur

BrassCopperEbonite

Paraffin waxSilk

LeadFur

woolglass

Increasing tendency to lose electrons

Increasing tendency to hold on to electrons

Whichever material is closer to the top holds electrons more tightly so will gain a negative charge.Whichever is closer to the bottom has a tendency to lose electrons so will gain a positive charge.

Page 3: Forces and Fields

Two Static ExamplesTwo Static ExamplesRubbing ebonite with fur

produces a negative charge on the ebonite and a positive charge on the fur.

Rubbing glass with silk produces a negative charge on the silk and a positive charge on the glass because the glass gives up electrons more easily.

Page 4: Forces and Fields

GroundingGroundingThe process of sharing charge with the earth. The earth can gain or donate electrons as needed to transfer a charge. The overall effect of this process is to make the object that comes into contact with the earth neutral.

The symbol for ground is

+ + + + + + + +

Earth

Conductive wire

electrons

Page 5: Forces and Fields

Three Ways Charge Can Be Three Ways Charge Can Be TransferredTransferred

1. Friction (also called abduction)2. Conduction – touching a charged

object to an neutral object3. Induction – bringing an charged

object near a neutral object to cause temporary charge separation which polarizes the neutral object

Page 6: Forces and Fields

Electrons in the paper are repelled to the most distant point leaving a localized positive charge near the negative comb.

Result – paper is attracted to the comb

When the comb is removed, electrons are redistributed in the paper.

Charge Migration

Page 7: Forces and Fields

InductionInductionSteps to charge by induction:1.Bring a charged object close to (but

not touching) a neutral object.2.Ground the neutral object.3.Remove the ground.4.Remove the charged object.(The previously neutral object will

retain a charge because of the grounding step.)

Page 8: Forces and Fields

Diagram of InductionDiagram of Induction

Page 9: Forces and Fields

The ElectroscopeThe Electroscope

A simple device used to detect a charge on an object

It does not identify the quantity of charge, only whether a charge is present. It can be used to detect the sign of the charged object with some additional steps, but not directly.

Page 10: Forces and Fields

Two TypesTwo Types1. Pith Ball ElectroscopeWhen pith balls are touched with a

charged object, the two balls acquire the same charge and therefore repel each other.

before After (repel)

Page 11: Forces and Fields

2. Gold Leaf/Foil Electroscope◦When the metal knob is touched with a

charged object, the leaves/foil will repel each other.

Metal knob

Insulator

Glass container

Metal rod

Gold leaves (touching)

Metal knob

Insulator

Glass container

Metal rod

Gold leaves (repelling)

Page 12: Forces and Fields

There are two ways to There are two ways to charge an electroscope.charge an electroscope.

Charging by CONDUCTIONTouch the ball with ebonite, (excess e’) and remove the

rod. Some e’ are transferred from the ebonite which makes the ball negative. The leaves are now both negative and will repel. The electroscope’s leaves will have the same charge as the object.

 Charging by INDUCTIONConnect a wire to the electroscope. Bring the ebonite

rod close to but do not touch the electroscope. The negative charges in the electroscope are repelled, and move through the wire into the ground, (grounding). This causes the remaining positive charges in the leaves to repel each other, therefore spreading the leaves. Keep the ebonite in place and remove the grounding wire. The electroscope stays positively charged. It will have an opposite charge to the object.