Electricity And Magnetism Continuous Charge Distributions .
Electricity and MagnetismContinuous Charge DistributionsFaraday CagesLana SheridanDe Anza CollegeJan 17, 2018
Last time electric field of a dipole continuous distributions of charge
Warm Up QuestionsVery far away from an electric dipole, the electric field decreases aswith distance from the dipole r as:1(A) r1(B) r 21(C) r 31(D) r 4
Warm Up QuestionsVery far away from an electric dipole, the electric field decreases aswith distance from the dipole r as:1(A) r1(B) r 21(C) r 31(D) r 4
Warm Up QuestionsVery far away from a uniform ring of charge, the electric fielddecreases as with distance from the dipole r as:1(A) r1(B) r 21(C) r 31(D) r 4
Warm Up QuestionsVery far away from a uniform ring of charge, the electric fielddecreases as with distance from the dipole r as:1(A) r1(B) r 21(C) r 31(D) r 4
Overview more fields from continuous charge distributions conductors in fields
dq1 ds!.r24"#0 r 2Example: Field from(22-11)a ring of charge (23.8 in2-11astextbook) ds1."#0 (z2 % R2)foreldg(22-12)zdE cos θdEθThe perpendicularcomponents justcancel but the parallelcomponents add.Pθzr ds R Vertical components? From eachcharge dq λ ds:dEz dE cos θ
dq1 ds!.r24"#0 r 2Example: Field from(22-11)a ring of charge (23.8 in2-11astextbook) ds1."#0 (z2 % R2)foreldg(22-12)zdE cos θdEθThe perpendicularcomponents justcancel but the parallelcomponents add.Pθzr ds R Vertical components? From eachcharge dq λ ds:dEz dE cos θ kλ dscos θ r2 kλ dsz 222(R z )R z2k z λ ds 2(R z 2 )3/2
dq1 ds!.r24"#0 r 2Example: Field from(22-11)a ring of charge (23.8 in2-11astextbook) ds1."#0 (z2 % R2)foreldg(22-12)zdE cos θdEθdEz The perpendicularcomponents justcancel but the parallelcomponents add.Pθzr ds R k z λ ds(R 2 z 2 )3/2There are 2πR-worth of little lengthsds. Adding the field for all together:ZZkzλdsEz dEz (R 2 z 2 )3/2 (R 2kqz z 2 )3/2since total charge q 2πRλ bydefinition.
mly Charged DiskExample: Field from a disk of charge (23.9 ins. textbook)Calculate the electricdqar axis of the disk and aRrx23.17 (Example 23.9) Amly charged disk of radius R.ctric field at an axial point Pted along the central axis, perular to the plane of the disk.PxdrWe already know the field contribution for a ring of charge.(dq 2πr σ dr)ry, the field at an axial point must be along the central axis.continuedJust add up rings of different radius.ZRExkx(2πr σ) dr2 x 2 )3/2(r0 x 2πkσ 1 R2 x2
Example: Field from a disk of charge (23.9 intextbook)mly Charged Disks. Calculate the electricar axis of the disk and adqRrx23.17 (Example 23.9) Amly charged disk of radius R.ctric field at an axial point Pted along the central axis, perular to the plane of the disk.Pxdrry, the field at an axial point must be along the central axis. Ex continuedx 2πkσ 1 R2 x2What happens if x while R is constant?What happens if R while x is constant?
ormlyConductors in Electric fieldschargereachConsider a neutral conductor placed in an electric field:d, proushes,arges,ch cirwhere –– – ––– –made–– 20, aller the–Fig. 24-20––E 0––– An uncharged conduc-
Conductors in Electric fieldsElectric fields exert forces on free charges in conductors.Each charge keeps moving until:1the charges reaches the edge of the conductor and can moveno further OR2the field is cancelled out!Inside a conducting object, the electric field is zero!
Effects of E-Fields: Sparking (Electrical Breakdown)Electric fields can cause forces on charges.If the field is very strong, it begins to accelerate free electronswhich strike atoms, knocking away more electrons forming ions.This starts a cascade, forming a spark.
Effects of E-Fields: Sparking (Electrical Breakdown)Electric fields can cause forces on charges.If the field is very strong, it begins to accelerate free electronswhich strike atoms, knocking away more electrons forming ions.This starts a cascade, forming a spark.The strength of the field where this happens is called the criticalfield, Ec , For air Ec 3 106 N/C.
Effects of E-Fields: Sparking (Electrical Breakdown)Electric fields can cause forces on charges.If the field is very strong, it begins to accelerate free electronswhich strike atoms, knocking away more electrons forming ions.This starts a cascade, forming a spark.The strength of the field where this happens is called the criticalfield, Ec , For air Ec 3 106 N/C.The air along the spark becomes a plamsa of free charges and canconduct electricity.Sparks look like bright streaks because the air molecules becomesso hot. Accelerating charges radiate, so lightning can also causeradio interference.
12E (kV/m)om the curve of Fig. 24-18a by differentiating with respect to r,Faradayrecallthat theCagesderivative of any constant is zero). The curve ofAconductingcan ofshieldinteriorfrom even verybe derivedfrom theshellcurvesFig. the24-18bby integratingwithstrongelectric fields.g Eq. 24-19.840Fig. 24-1rge sparkdy and thenross thet tire (noteving the pered. (Courtesyric1Photo from Halliday, Resnick, Walkerinside andcal shell oE(r) for t
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Summary more continuous charge distributions conductors in electric fieldsQuiz on Friday, Jan 19.Homework Collected homework 1, posted online, due on Monday, Jan 22.Serway & Jewett: PREVIOUS: Ch 23, Probs: 45, 71, 84 NEW!: Ch 23, Probs: 75, 83
Charge q C Linear charge density l C/m Surface charge density s C/m2 Volume charge density r C/m3 Table 22-2 Fig. 22-10 A ring of uniform positive charge.A differential element of charge occupies a length ds (greatly exaggerated for clarity).This element sets up an electric Þeld at point P.T
Magnetism (Section 5.12) The subjects of magnetism and electricity developed almost independently of each other until 1820, when a Danish physicist named Hans Christian Oersted discovered in a classroom demonstration that an electric current affects a magnetic compass. He saw that magnetism was related to electricity.
Students will be able to explain how electricity and magnetism work together in electric motors and generators. Anticipatory Set Students have learned about electricity, electric circuits, voltage, and current. They are familiar with how to connect circuit elements. Electricity and magnetism are closely related.
In Electricity and Magnetism, students study a variety of topics including electricity, circuits and magnetism through the use of student conducted laboratory, field investigations, and scientificmethods . Textbook: Any state adopted Physics textbook and an inquiry-based Physics lab manual.
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The Princeton Review Practice SAT Physics Subject Test 1 431 GO ON TO THE NEXT PAGE 27. Four point charges are labeled Charge 1, Charge 2, Charge 3, and Charge 4. It is known that Charge 1 attracts Charge 2, Charge 2 repels Charge 3, and Charge 3 attracts Charge 4. Which
What is the difference between static electricity and current electricity? Static electricity is stationary or collects on the surface of an object, whereas current electricity is flowing very rapidly through a conductor. The flow of electricity in current electricity has electrical pressure or voltage. Electric charges flow from an areaFile Size: 767KB
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