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GENERAL PHYSICS B

Dr Maher O. El-Ghossain,

Departmentof

PhysicsThe Islamic University of Gaza

Gaza, Palestine,ghossain@mail.iugaza.edu

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CHAPTER ONE

ELECTRIC FORCE

AND

ELECTRIC FIELD

(CHAPTER 23)

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Charge Properties1. TWO CHARGES POSITIVE AND NEGATIVE2. THE FORCE BETWEEN THEM ATTRACTION OR

REPULSION (different and same chrges)3. CONSERVATION4. QUANTIZATION

CHARGE TRANSFERRED BY CONDUCTION OR INDUCTION

1. CHARGE PRODUCED BY RUBBING OR CHARGING

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+ -

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ELECTRICAL PROPERTIES OF MATTER

• CONDUCTOR

• INSULATOR

• SEMICONDUCTOR

• SUPERCONDUCTOR

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Quiz 1:If you rub an inflated balloon against your hair, the two materials attract each other, as shown in Figure. Is the amount of charge present in the balloon and your hair after rubbing (a) less than, (b) the same as, or (c) more than the amount of charge present beforerubbing?

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Charging a metallic object by induction (that is, the two objects never touch each other). (a) A neutral metallic sphere, with equal numbers of positive and negative charges.(b) The charge on the neutral sphere is redistributed when a charged rubber rod is placed near the sphere. (c) When the sphere is grounded, some of its electrons leave through the groundwire. (d) When the ground connection is removed, the sphere has excess positive charge that is nonuniformly distributed. (e) When the rod is removed, the excess positive charge becomes uniformlydistributed over the surface of the sphere

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ELECTRIC FORCE :

)2.1(ˆ221 r

rqqkF =

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+_

q1 r q2

F12 F21

FFαα 11/r/r22And F And F αα qq1 1 qq22

k= k= 88..99 99 x x 10109 9 N MN M22/ C/ C22,where k=,where k=11//44ππєєoo and and єєooareare the the permittivity of free space, which equal to:permittivity of free space, which equal to:єєoo = = 88..85 85 x x 1010^̂--12 12 C C 22/ N. M/ N. M22qq1 1 : first charge, q: first charge, q2 2 : second charge ,: second charge ,ř: unit vector in the direction of r.ř: unit vector in the direction of r.

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Example 1.1The electron and proton of a hydrogen atom are separated(on the average) by a distance of approximately .Find the magnitudes of the electric force and the gravitational force

between the two particles.Solution From Coulomb’s law

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Example 1.2

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Consider three point charges located at the corners of a righttriangle as shown in Figure, where

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EXAMPLE 1.4Three point charges lie along the x axis as shown in Figure. The

positive charge is at x = 2.00 m, the positive charge is at the origin, and the resultant force acting on q3 is zero. What is the x coordinate

of q3?

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EXAMPLE 1.5

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1.4

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ELECTRIC FIELD OF POINT CHARGE

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EXAMPLE 1.6

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EXAMPLE 1.7

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1.5

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