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Unformatted text preview: Electric Forces and Electric Fields 1 – Properties of Electric Charges • Electric charge is an intrinsic property of matter, inherent in its atomic structure. electron charge: q =- e proton charge: q = + e with elementary charge: e = 1 . 60 · 10- 19 Coulomb • The earliest studies of electricity were conducted by the Greeks ( ≈ 570 B.C. Thales of Milet): amber (greek: electron ) attracts small objects after being rubbed with wool • Experiments demonstrate that there are two kinds of electric charges: positive and negative (Benjamin Franklin [1706 – 1790]) Dr.Wackeroth Spring 2005 PHY102A Electric Forces and Electric Fields • l i k e c h a r g e s r e p e l o n e a n o t h e r a n d u n l i k e c h a r g e s a t t r a c t o n e a n o t h e r • objects become charged through contact with another already charged object or by induction (no contact). • When charging an object negative charge is transferred from one object to the other. • electric charge is conserved: → the sum of all electric charges in the universe does not change → when an electrically charged object is created the same amount of negative and positive charge is produced Dr.Wackeroth Spring 2005 PHY102A Electric Forces and Electric Fields 2 – Conductors and Insulators Substances are classified in terms of their ability to con- duct electric charge: • Conductors: materials in which electric charges move freely E x a m p l e s : copper, aluminum, in general all metals • Insulators: materials in which electric charges do not move freely...
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