Electrical Charges and Coulomb’s Law Phys 2180 Lecture (1) 1.
Lecture 1-Coulomb_s Law
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Transcript of Lecture 1-Coulomb_s Law
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
Engineering Electromagnetics
LECTURE 1: Coulombs Law
Instructor: Sir Tim
Summer Term
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Coulombs Law
ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
POINT CHARGES
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
ATOMIC MODEL
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
VALENCE
The NUMBER OF ELECTRONS in THEOUTERMOST SHELL determines thevalence of the atom
The outermost shell is called theVALENCE SHELL
The electrons residing in the outermostshell is called VALENCE ELECTRONS
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
Electrostatics
Deals with the phenomena due to theATTRACTIONS OR REPULSIONS OFELECTRIC CHARGES that are NOTMOVING.
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
Static Electricity
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
Coulombs Law
Coulombs First Law of Electrostatics The size of the force of attraction or repulsion
between two charges is DIRECTLYproportional to the value of the charge
Coulombs Second Law of Electrostatics The size of the force varies INVERSELY asthe square of the distance between the twocharges
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
Mathematical Form
k = 1/(4pi),(for air o = shift constant 32)
F force in newtons
Q1 and Q2 charge in coulombs
r distance bet. two charges in meters
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
NATURE OF CHARGES
LIKE charges REPEL
UNLIKE charges ATTRACT
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
ELECTRIC FIELD
Defined as the force per unit positivecharge that would be experienced by astationary point charge in a given locationin a field
The space between and around thecharged bodies where their influence is felt
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
ELECTRIC FIELD
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
ELECTRIC FIELD
k = 1/(4pi),(for air o = shift constant 32)
E electric field intensity in V/m orN/C
Q charge in coulombs r distance in meters
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
Problem 1
Point charges 1 mC and -2 mC are locatedat (3, 2, -1) and (-1, -1, 4) respectively.Calculate the electric force on a 10-nCcharge located at (0, 3, 1) and the electricfield intensity at that point.
Ans: F = -6.507ax 3.817ay + 7.506az mN
E = -650.7ax 381.7ay 750.6az kV/m
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
Problem 2
Two point charges of equal mass m, chargeQ are suspended at a common point by twothreads of negligible mass and length l.Show that at equilibrium, the inclinationangle of each thread to the vertical isgiven by
2 = 162 sin2 tan
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
Problem 3
A practical application of electrostaticsseparation of solids. Assuming zero initialvelocity and displacement, determine theseparation between the particles after falling80 cm. Take E = 500 kV/m and Q/m = 9C/kg for both positively and negativelycharged particles.
Ans: 73.4 cm
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Coulombs Law
ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
CHARGE DISTRIBUTION
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
VOLUME CHARGE DISTRIBUTION
=
where:
V is the volume charge density; and
Q is the total charge within some finite volume
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
FIELD OF A LINE CHARGE
=2
where:
L is the line chargedensity
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
FIELD OF A SHEET OF CHARGE
=2
where:
S is the surface chargedensity
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
Problem 1
Find the force on a point charge 50 C at (0,0, 5) m due to a circular disk with surfacecharge density of s = 20 C/m
2 and 5m, z = 0 m.
Ans: F = 16.5az N
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
Problem 2
The finite sheet 0 1, 0 1 on the z= 0 plane has a charge density =
(2 + 2 + 25)3
2 nC/m2. Find:(a) the total charge on the sheet(b) the electric field at (0, 0, 5)(c) the force experienced by a -1 mC charge
located at (0, 0, 5)
Ans: (a) Q = 33.15 nC(b) E = -1.5ax, -1.5ay, 11.25az V/m(c) F = 1.5ax, 1.5ay, -11.25az mN
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
Problem 3
Determine E at (2, 0, 2) m due to threestandard charge distributions as follows: auniform sheet at x = 0 m with s1 = (1/3)nC/m2, a uniform sheet at x = 4 m with s2= (-1/3) nC/m2, and a uniform line at x =6 m, y = 0 m with l = -2 nC/m.
Ans: E = 21ax V/m
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ECE Department, TUP Manila Engineering Electromagnetics Timothy M. Amado, ECE Summer
Thank you.
Lecture 1: Coulomb's Law
Engineering Electromagnetics
Timothy M. AmadoFaculty, Electronics Engineering Department
Technological University of the Philippines Manila