STATIC ELECTRICITY II:Charging neutral objects

S1-3-07 Construct one or more electrostatic apparatus and explain how they function using the particle model of electricity.

KEY WORDSElectroscope GroundingConduction Induction

Electroscope: a tool for determining whether or not an electrical charge is present in an object.

It provides 3 kinds of measurement: – detects the presence of a charge– determines the type of charge (+ or – )– determines the amount of charge

We will look at two kinds of electroscopes: pith ball and foil leaf

Polarization is NOT permanent – when the charged object moves away – electrons move back to neutral, leaves close

Leaf Electroscopes

• Polarization is “inducing” a temporary charge

A permanent charge can be placed on an object by:1. Conduction – charging by contact2. Induction – charging with grounding

1. Conduction• Electric charge transfers from a charged object

to a neutral object by touching End result: the neutral object gains the same

charge as the object

END: Both objects are overall (-) charged (repulsion)

1. Charged rod

2. Polarization in pith ball (attraction)

3. Pith touches rod – electrons are transferred

e-

Negative charge (excess e-)

Negative charge (excess e-)

(–) CONDUCTION

END: Both objects are overall (+) charged (repulsion)

1. Charged rod

2. Polarization in pith ball (attraction)

3. Pith touches rod – electrons are transferred

e-

Positive charge (lost e-)

Positive charge (lost e-)

(+) CONDUCTION

• Polarization is “inducing” a temporary charge

1. Induction• Grounding is used to place a permanent electric charge on a polarized neutral object

End result: the neutral object gains the opposite charge as the object

The charged object and neutral object DO NOT make contact

–––––

++

++

+

–

–––

– –

–

Grounding is used to “reset” or neutralize a charged object

To “ground” means connect the object to Earth:

• Electrons move up from Earth into an object, or move down from the object into Earth (as needed)

END: Objects have overall opposite charge

1. Charged rod is close – not touching

2. Polarization in object - GROUNDING

3. Electrons repelled off towards Earth

e-

Negative charge (excess e-)

Positive charge (lost e-)

(–) INDUCTION

END: Objects have overall opposite charge

1. Charged rod is close – not touching

2. Polarization in object - GROUNDING

3. Electrons attracted over from Earth

e-

Positive charge (lost e-)

Negative charge (gained e-)

(+) INDUCTION

Triboelectric – by frictionSTART: two neutral objects • friction causes electron transferEND: one becomes (-) charged, other (+) charged

Conduction – by contactSTART: neutral object and a charged object• polarization and then contact causes electron transfer END: Both objects have the same charge

Induction – with groundingSTART: Charged object brought close to neutral object• polarization and then grounding causes electron

transfer END: Both objects have the opposite charge

CAN YOU ANSWER THESE QUESTIONS?S1-3-07:How does an electrostatic apparatus work to identify charge?

KEY WORDSElectroscope ConductionInduction Grounding