Electricity and Magnetism: A Historical Overview of Electric Charges and Their Properties , Study notes of Physics

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Chapter 23 Electric Fields

„

Electric charges

„

Charging by induction

„

Coulomb’s law

„

Electric field

„

Electric calculation

„

Electric field lines

„

Motion of charged particles in uniform

electric field

Electricity and Magnetism,Some History

„

Many applications^ „

It is unimaginable nowadays if there is no E&M „

Macroscopic and microscopic

„

2000 BC^ „

Chinese documents suggest that magnetism wasobserved as early as 2000 BC

„

700 BC^ „

Greeks observed electrical and magneticphenomena as early as 700 BC „

Experiments with amber and magnetite

Electricity and Magnetism, SomeHistory, 3

„

1819 „

Hans Oersted found a compass needledeflected when near a wire carrying anelectric current

Electricity and magnetism are related phenomena

Electricity and Magnetism, SomeHistory, 4 „

Michael Faraday andJoseph Henry showedthat when a magnet ismoved near loop of wire,an electric current isproduced in the wire loop.

Joseph Henry 1797^ Joseph Henry

1797

-1878^1878 -

Electricity and Magnetism, SomeHistory, 6 „

1909 „

Robert Millikan (1868-1953) discovered thatelectric charge is always an integer times somebasic charge (now known as the charge ofelectron or proton).

Electric Charges „

There are four fundamental forces of nature^ „

Gravity

„

Electromagnetic

„

Strong

„

Weak

http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html

Electric Charges, 2

„

The rubber rod (rubbedwith fur) is negativelycharged „

The glass rod (rubbedwith silk) is positivelycharged „

The two rods will attract

Fur

Silk

Electric Charges, 3 „^

The rubber rod isnegatively charged

„

The second rubberrod is alsonegatively charged

„

The two rods willexpel

Conservation of Electric Charges

„

A glass rod isrubbed with silk^ „

Electrons aretransferred from theglass to the silk „

Each electron adds anegative charge tothe silk „

An equal positivecharge is left on therod

Quantization of Electric Charges

„

The electric charge,

q

, is said to be quantized

„

q

is the standard symbol used for charge as a variable „

Electric charge exists as discrete packets „

q

Ne „^

N

is an integer

„^

e

is the fundamental unit of charge (Millikan, 1909) „^

| e

| = 1.6 x 10

C

„^

Electric:

q

= -

e

„^

Proton:

q

= +

e