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![Page 1: Electricity Lecture Series email: jjnita@salam.uitm.edu.my; drjjlanita@hotmail.com jjnita@salam.uitm.edu.mydrjjlanita@hotmail.comjjnita@salam.uitm.edu.mydrjjlanita@hotmail.com.](https://reader035.fdocuments.net/reader035/viewer/2022070323/56649dc95503460f94abf0fc/html5/thumbnails/1.jpg)
Electricity Lecture SeriesElectricity Lecture Series
email: email: [email protected]@salam.uitm.edu.my; ; [email protected]@hotmail.comhttp://www3.uitm.edu.my/staff/drjj/http://www3.uitm.edu.my/staff/drjj/
Applied Sciences Education Research Group (ASERG)
Faculty of Applied SciencesUniversiti Teknologi MARA
Charges Electric Charges Electric Fields, Potential Fields, Potential and Capacitorsand Capacitors
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Copyright DR JJ,FSG, UiTM 2
Electric ChargesElectric Charges
1. Explain the gravitational forces acting on any object.
2. Mathematically represent the gravitational force and describe its impact on physical events.
3. Describe existence of electrical charges in matter and its quantization property.
4. Sketch and explain the charging by induction and charging by contact
5. Mathematically represent forces acting between electrical charges (Coulomb’s Law)
Objectives:
Objectives:
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Copyright DR JJ,FSG, UiTM 3
Electric ChargesElectric Charges
6. Represent forces acting between charges both pictorially and vectorially.
7. Describe and explain gravitational and electric field.
8. Derive mathematical relations for electric field of point charges, line charges and surface charges and the use of Gaussian surface.
9. Describe and explain capacitors and its purpose.
Objectives:
Objectives:
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Copyright DR JJ,FSG, UiTM 4
Electric ChargesElectric Charges
10.Write mathematical relations for parallel plate capacitors related to capacitance, potential difference, its geometrical dependence, and electric field it can store.
11.Obtain energies stored by capacitors.
12.Explain and pictorially and graphically represent the charging and discharging of capacitors.
Objectives:
Objectives:
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Copyright DR JJ,FSG, UiTM 5
Electric ChargesElectric Charges
13.Describe, draw and obtain resultant capacitances for capacitors connected in parallel and in series respectively.
14.Solve conceptual and numerical problems associated with capacitors.
Objectives:
Objectives:
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Copyright DR JJ,FSG, UiTM 6
Electric ChargesElectric Charges
MatterMatter: made up of atoms and molecules
Charged objectCharged object: imbalance number of electrons & protonsPositively chargedNegatively charged
AtomAtom: made up of nucleus, protons and electrons
ConductorsConductors: charges can move freelyInsulatorsInsulators: charges cannot move freely
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Copyright DR JJ,FSG, UiTM 7
18.1 18.1 The Origin of ElectricityThe Origin of ElectricityCutnell & Johnson 7ECutnell & Johnson 7E
The electrical nature of matter is inherentin atomic structure.
kg10673.1 27pm
kg10675.1 27nm
kg1011.9 31em
C1060.1 19e
coulombs
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Copyright DR JJ,FSG, UiTM 8
Electric ChargesElectric Charges
Charge quantizationCharge quantization: charges exist in multiples of an elementary charge, the charge of an electron
,..2, eeNeq where N are the number of electrons & the elementary charge e is e =1.6 x 10-19 CNumber of charges in 1 C?? N=q/e =1 C/1.6 x 10-19 CN = 6.25 x 1018
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Copyright DR JJ,FSG, UiTM 9
18.2 18.2 Charged Objects and the Electric ForceCharged Objects and the Electric ForceCutnell & Johnson 7ECutnell & Johnson 7E
LAW OF CONSERVATION OF ELECTRIC CHARGE
During any process, the net electric charge of an isolated system remains constant (is conserved). Total number of negative charges (electrons) and positive charges (protons) must be equal
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Copyright DR JJ,FSG, UiTM 10
18.3 18.3 Conductors and InsulatorsConductors and InsulatorsCutnell & Johnson 7ECutnell & Johnson 7E
Not only can electric charge exist on an object, but it can also movethrough and object.
Substances that readily conduct electric charge are called electricalConductors – copper, iron, gold, water, human body
Materials that conduct electric charge poorly are called electricalInsulators – plastic, wood, rubber
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Copyright DR JJ,FSG, UiTM 11
18.4 18.4 Charging by ContactCharging by ContactCutnell & Johnson 7ECutnell & Johnson 7E
Charging by contact.
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Copyright DR JJ,FSG, UiTM 12
18.4 18.4 Charging by InductionCharging by InductionCutnell & Johnson 7ECutnell & Johnson 7E
Charging by induction.
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Copyright DR JJ,FSG, UiTM 13
18.4 18.4 Charging by Contact and by InductionCharging by Contact and by InductionCutnell & Johnson 7ECutnell & Johnson 7E
The negatively charged rod induces a slight positive surface chargeon the plastic.
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Copyright DR JJ,FSG, UiTM 14
Electric Forces-Coulomb’s LawElectric Forces-Coulomb’s Law
Gravitational forces (Law of Gravitational forces (Law of Gravitation)Gravitation): Earth pulls on the moon and vice-versa. Any 2 objects will always exert and feel attractive gravitational forces. They exert with same magnitude. Moon feels attraction because it is in the earth’s gravitational field.
2r
MmF earthmoon
earth to due moon
F is inversely proportional to square of separation between masses.
2r
mMF moonearth
moon to due earth
r Fme
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Copyright DR JJ,FSG, UiTM 15
Electric Charges-ForcesElectric Charges-ForcesGravitational forcesGravitational forces:
F is inversely proportional to square of separation between masses.
r, m r2, m2 F, N Ratios of F
10 100 F1=Gm1m2/100 F1/F2=4
20 400 F2=Gm1m2/400 F1/F3=9
30 900 F3=Gm1m2/900 F2/F3=9/4
2r
MmGF earthmoon
earth to due moon r F12
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Copyright DR JJ,FSG, UiTM 16
18.2 18.2 Charged Objects and the Charged Objects and the Electric ForceElectric Force
Cutnell & Johnson 7ECutnell & Johnson 7E
Like charges repel and unlike charges attract each other.
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Copyright DR JJ,FSG, UiTM 17
18.5 18.5 Coulomb’s LawCoulomb’s Law Cutnell & Johnson 7E Cutnell & Johnson 7E
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Copyright DR JJ,FSG, UiTM 18
Electric Charges-Coulomb’s LawElectric Charges-Coulomb’s Law
Electric forcesElectric forces: Charged objects exert electric forces on each other. Can be attractive or repulsive. Like charges repel. Unlike charges attract.
221
221
12 r
qqk
r
qqFF 2 to due 1
+
+
r F21
q1=e
q2=2e
20
122
1221 4 r
r
qqkFF 1 to due 2
constant electrick 04
1
0 = permittivity of free space0 = 8.85 x 10-12 C2/Nm2
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Copyright DR JJ,FSG, UiTM 19
18.5 18.5 Coulomb’s LawCoulomb’s Law Cutnell & Johnson 7E Cutnell & Johnson 7E
COULOMB’S LAW
The magnitude of the electrostatic force exerted by one point charge on another point charge is directly proportional to the magnitude of the charges and inversely proportional to the square of the distance between them.
221
r
qqkF
229 CmN1099.841 ok
2212 mNC1085.8
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Copyright DR JJ,FSG, UiTM 20
18.5 18.5 Coulomb’s LawCoulomb’s Law Cutnell & Johnson 7E Cutnell & Johnson 7E
Example 4 Three Charges on a Line
Determine the magnitude and direction of the net force on q1.
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Copyright DR JJ,FSG, UiTM 21
Nm
CCCmN
r
qqkF
22
7.220.0
100.4100.31099.82
669
221
12
Nm
CCCmN
r
qqkF
22
4.815.0
100.7100.31099.82
669
231
13
5.7NN4.8N7.21312 FFF
18.5 18.5 Coulomb’s LawCoulomb’s Law Cutnell & Johnson 7E Cutnell & Johnson 7E
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Copyright DR JJ,FSG, UiTM 22
Electric Point ChargesElectric Point Charges
Electric forcesElectric forces: repulsive forces since both are positively charged.
212
21)2/(r
qqkFF 1 to due 2
4/212
r
qqkF 21
2124
r
qqkF 21
212
21r
qqkFF 1 to due 2
+
+
r F
q1=e
q2=2e
Fset1 Fset2<
+
+
r/2 F
q1=e
q2=2e
SET 2
Is accset1 bigger or smaller than accset2??
down
down
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Copyright DR JJ,FSG, UiTM 23
Electric Point ChargesElectric Point Charges
Electric forcesElectric forces: attractive forces since opposite charges
212
r
qqkF 21
2
242
r
ekF 21
2
2
2
422
r
ek
r
eekF 21
-
+
r F
q1=2e
q2=2e
Fset1 Fset2<
-
+
r F
q1=4e
q2=2e
2
28
r
ekF 21
Is accset1 bigger or smaller than accset2??
up
up
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Copyright DR JJ,FSG, UiTM 24
Electric Point ChargesElectric Point Charges
Electric forcesElectric forces: Determine forces acting on charge 2
2232 22
r
eek
r
qqkF 23
2
2
2
2
2
2 844
r
ek
r
ek
r
ekFF 3 21 2
2
2
2
422
r
ek
r
eekF 21
-
+
r F
q1=2e
q3=2eWhat is the magnitude and direction of net force acting on q2?
+ q2=2e
r
up
up
up
What is the magnitude and direction of acceleration of q2?
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Copyright DR JJ,FSG, UiTM 25
Electric Point ChargesElectric Point Charges
Electric forcesElectric forces: Determine forces acting on charge 2
2232 22
r
eek
r
qqkF 23
2
2
2
2
2
2 54
r
ek
r
ek
r
ekFF 3 21 2
2
2
2212
4
4
2
22
r
ek
r
eek
r
qqkF 21
-
+
2r F
q1=2e
q3=2e
What is the magnitude and direction of acceleration of q2?
+ q2=2e
r
up
up
up
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Copyright DR JJ,FSG, UiTM 26
18.5 18.5 Coulomb’s LawCoulomb’s Law Cutnell & Johnson 7E Cutnell & Johnson 7E
Example 3 A Model of the Hydrogen Atom
In the Bohr model of the hydrogen atom, the electron is in orbit about the nuclear proton at a radius of 5.29x10-11m. Determine the speed of the electron, assuming the orbit to be circular.
221
r
qqkF
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Copyright DR JJ,FSG, UiTM 27
18.518.5 Coulomb’s LawCoulomb’s Law Cutnell & Johnson 7E Cutnell & Johnson 7E
N1022.8
m1029.5
C1060.1CmN1099.8 8211
219229
2
21
r
qqkF
sm1018.2
kg109.11
m1029.5N1022.8 631-
118
mFrv
rmvmaF c2
For circular motion & using Newton’s 2nd law of motion
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Copyright DR JJ,FSG, UiTM 28
Electric Point ChargesElectric Point Charges
Electric forcesElectric forces: Determine forces acting on charge 2
2232 22
r
eek
r
qqkF 23
2
2
2
2
2
2 34
r
ek
r
ek
r
ekFF 3 21 2
2
2
2212
4
4
2
22
r
ek
r
eek
r
qqkF 21
+
+
2r F12
q1=2e
q3=2e
What is the magnitude and direction of acceleration of q2?
+ q2=2e
r
down
up
up
F21
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Copyright DR JJ,FSG, UiTM 29
Electric Point ChargesElectric Point Charges
Electric forcesElectric forces: Determine forces acting on charge 2
+
+
2r
q1=2e
q3=2e
-
r
+ q4=2e
q2=e
+ q5=2e
2r
2r
F21
F23
F24
F25
F24
F25
F25sin25
F24sin24
F2
4co
s2
4
F2
5co
s2
5
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Copyright DR JJ,FSG, UiTM 30
Electric Point ChargesElectric Point ChargesElectric forcesElectric forces: Determine forces acting on charge 2
2r
2r
Pythagoras theorem: Charge 2 & 4 is separated by the distance:
2
2
2221
12
22
2
r
ek
r
eek
r
qqkF 21
2
2
2223
32 22
r
ek
r
eek
r
qqkF 23
up
down
2
2
2
2
2224
42
48
2
22
2
r
ek
r
ek
r
eek
r
qqkF 24
228)2()2( 22224 rrrrr
Charge 2 & 5 is separated by the distance:
55)2( 22225 rrrrr
2
2
2
2
2225
52
5
2
5
2
5
2
r
ek
r
ek
r
eek
r
qqkF 25
2e 2e
r
2r
2e 2e
-e
r 24 = ??
r25 = ??
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Copyright DR JJ,FSG, UiTM 31
Electric Point ChargesElectric Point ChargesElectric forcesElectric forces: Determine forces acting on charge 2
2
2
2212
22
2
r
ek
r
eek
r
qqkF 21
2
2
2232 22
r
ek
r
eek
r
qqkF 23
up
down
2
2
2
2
2242
48
2
22
2
r
ek
r
ek
r
eek
r
qqkF 24
2
2
2
2
2252
5
2
5
2
5
2
r
ek
r
ek
r
eek
r
qqkF 25
2
1
22
2cos 24
r
r
2
1
22
2sin 24
r
r
5
1
5cos 25
r
r
5
2
5
2sin 25
r
r
Thenup
r
ekF y24 ;
24 2
2
right r
ekF x24 ;
24 2
2
down r
ekF y25 ;
54 2
2
right r
ekF x25 ;
52 2
2
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Copyright DR JJ,FSG, UiTM 32
Electric Point ChargesElectric Point ChargesElectric forcesElectric forces: Determine forces acting on charge 2
down r
ekFFFFF yy 25242321y ;
54
1
24
12
2
12
2
right r
ekFFF xx 2524x ;
52
1
24
12
2
22
yx FFF Then,
22
2
2
54
1
24
1
2
3
52
1
24
1
r
ekF Then,
F
Fx
Fy
54
1
24
123
52
1
24
1
naT
Take the arctan of theta to determine the force direction
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18.5 18.5 Coulomb’s LawCoulomb’s Law Cutnell & Johnson 7E Cutnell & Johnson 7E
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Elrctric field & forcesElrctric field & forcesAssignment: Due Aug 3Assignment: Due Aug 3rdrd 2006. 2006.
Chap 18Chap 18Exercises from the back of chapter.1,3,5,9, 13, 17,70, 71, 75Submit all