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Electricity Lecture SeriesElectricity Lecture Series
email: email: [email protected]@salam.uitm.edu.my; ; [email protected]@hotmail.comhttp://http://drjj.uitm.edu.mydrjj.uitm.edu.my
Applied Sciences Education Research Group (ASERG)Faculty of Applied SciencesUniversiti Teknologi MARA
Charges & ChargingCharges & Charging
Electric ChargesElectric Charges
1. Describe existence of electrical charges in matter its magnitude, mass, its relative masses, its charges, its quantization property and its conservation property.
2. Apply the quantization and conservation property for certain charging and discharging process
3. Sketch and explain charging by induction and charging by contact numerically and diagrammatically.
Objectives:
WEB
LLOs
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Electric ChargesElectric Charges
Experimental Results on Experimental Results on Atomic StructureAtomic StructureMatterMatter: made up of atoms and molecules
Charged objectCharged object: imbalance number of electrons & protonsPositively charged (lost electrons)Negatively charged (gain electrons)
AtomAtom: made up of nucleus, protons and electrons
ConductorsConductors: charges can move freely
InsulatorsInsulators: charges cannot move freely
WEB
LLOs
18.1 18.1 The Origin of ElectricityThe Origin of ElectricityCutnellCutnell & Johnson 7E& Johnson 7E
The electrical nature of matter is inherentin atomic structure.
kg10673.1 27−×=pm
kg10675.1 27−×=nm
kg1011.9 31−×=em
C1060.1 19−×=ecoulombs
How massive is the proton compared to an electron? Use proportional reasoning method to determine the answer.
WEB
LLOs
3
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
Number of charges in 1 μC?? N=q/e =1 μ C/1.6 x 10-19 CN = 6.25 x 10-18
WEB
LLOs
Charges, charging, electrical force & discharging
WEB
LLOs
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Charges, charging
WEB
LLOs
Charges, charging, electrical force
WEB
LLOs
5
Charges & charging
WEB
LLOs
Charges, charging, electrical force & discharging
6
Charges, charging, electrical force & discharging
Charges, charging, electrical force & discharging
7
Charges, charging, electrical force & discharging
Charges, charging, electrical force & discharging
8
Charges, charging, electrical force & discharging
Charges, charging, electrical force & discharging
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Charges, charging, electrical force & discharging
Charges, charging, electrical force & discharging
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Charges, charging, electrical force & discharging
18.4 18.4 Charging by ContactCharging by ContactCutnellCutnell & Johnson 7E& Johnson 7E
Charging by contact.
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18.4 18.4 Charging by InductionCharging by InductionCutnellCutnell & Johnson 7E& Johnson 7E
Charging by induction.
Charges, charging, electrical force & discharging
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Charges, charging, electrical force & discharging
18.2 18.2 Charged Objects and the Electric ForceCharged Objects and the Electric ForceCutnellCutnell & Johnson 7E& 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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Charge Conservation
A5q
B-3q
A2q
B0q
Aq
Bq
A5q
B-3q
C3q
Shown are conducting spheres each of charges 5q, -3q and 5q
What is the total charge on the spheres?
Sphere A touches sphere B and then separated.
What is the total charge after the process above, the charge on each individual sphere?
Charge Conservation
Bq
C3q
B2q
C2q
Aq
Bq
C3q
Shown are conducting spheres each of charges 5q, -3q and 5q
Sphere B touches sphere C and then separated.
What is the total charge after the process above, the charge on each individual sphere?
What is the total charge on the spheres?
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18.4 18.4 Charging by Contact and by InductionCharging by Contact and by InductionCutnellCutnell & Johnson 7E& Johnson 7E
The negatively charged rod induces a slight positive surface chargeon the plastic.
Electric Point ChargesElectric Point ChargesElectric forcesElectric forces: Determine forces acting on charge 2
2232 22
reek
rqqkF 23 ==
→
2
2
2
2
2
2 54rek
rek
rekFF 3 21 2 =+=+
→→
( ) 2
2
2212
44
222
rek
reek
rqqkF 21 ===
→-
+
2r F
q1=2e
q3=2e
What is the magnitude and direction of acceleration of q2?
+ q2=2e
r
up
up
up