week 1 - charge, conductors, insulators, and induction

8/11/2019 Week 1 - Charge, Conductors, Insulators, And Induction

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F1005 ELECTRICITY AND MAGNETISMF1005 ELECTRICITY AND MAGNETISM

CHARGE


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Static Electricity


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Attraction and Repulsion

Two rubber rodsrubbed with fur:REPEL

Two glass rodsrubbed with silk:REPEL

A glass rod rubbed

with silk and arubber rod rubbedwith fur: ATTRACT


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Attraction and Repulsion

Convention createdby Ben Franklin: Glass rod

positively charged Rubber rod

negatively

charged.


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Triboelectric Series

There are two classes of

materials. Ones thattake on a positive chargeand ones that take on anegative charge.


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Matter is made up of atoms An atom consist of

Electron carries a negative chargeProton carries a positive charge

Neutron caries no charge

ElectronsNucleusprotons

&neutrons

Atoms


7/22F1005 ELECTRICITY AND MAGNETISMF1005 ELECTRICITY AND MAGNETISM

Charge Electric charge (Q) is a physical property of matter.

The unit of charge is the coulomb (C), which is the amountof charge carried by 6.24 10 8 electrons

Like chargesrepel each other

--

+ +

Opposite chargesattract each other

+ -



Properties of charge Conservation of Charge

The total charge in an isolated system always remainsthe same.

Quantization of charge.The electric charge is described as multiples of certainunit of charge.

The charge of an electron is: = 1.6 10 C The charge of a proton is : = +1.6 10 C

The charge of a neutron is: = 0


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Conductors and Insulators

The electrons in the inner shells and in filledshells are held to the atom very strongly howeverthe electrons in the incomplete outer shells(valence electrons) are held weakly. Atoms andelements with strong outer shells are insulators,

atoms with weak outer shells are conductors(metals).



Conductors and Insulators



Last Class Charge

Static electricity Like charges Repel Opposite charges Attract The unit of charge is the coulomb Charge is quantized Charge is conserved Conductors and Insulators Charging by induction



Charging by Induction1. A charged rod is brought

close to two conductingspheres

2. The charged rod repelsthe positive charges andattracts the negativecharges

3. This pushes the positive

charges into the farsphere and pulls thenegative charges into theclose sphere



Charging by Induction1. The two spheres are

moved out of contact withthe charged rod still inplace

2. The charged rod ismoved away

3. Now the spheres arecharged



Ground

The earth can be thought of as an extremely largeconducting sphere (in most cases infinitely large).Because it is so large when you add charge to it or takecharge away it stays neutral.



Ground

The wall sockets of mosthouses have a ground.This is often used as asafety measure inelectronic devices toensure that no largecharges are allowed tobuild in locations that aperson may touch.



Dipole

A dipole is somethingthat has positive charge

on one side and anegative charge on theother side. - +



Dipole

A dipole is somethingthat has positive charge

on one side and anegative charge on theother side. A watermolecule is an example

of a molecule with apermanent dipolemoment.



Van de Graaff Generator

The Van de Graaff generator uses theconcepts we have been learning tocreate an extremely large charge on a

metal dome. Van de Graaff generators have been

used as particle accelerators I used a Van de Graaff generator for

my research at Lehigh Universitystudying the effects of radiation onscintillating fibers.




1. Hollow metal sphere2. Upper electrode3. Upper roller4. Side of belt with positive

charge5. Opposite side of belt with

negative charge6. Lower roller7. Lower electrode8. Spherical device9. Spark




http://youtu.be/XIxwYOMCCmE

Demonstrations


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Coulombs Law

=

~9 10 NmC

=1

4

=

week 1 - charge, conductors, insulators, and induction

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