Slide 1Object A has a charge of +2 µC, and object B has a charge of +6 µC. Which statement is true: (a) FAB = –3FBA, (b) FAB = –FBA, or (c) 3FAB = –FBASlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Outline for TodayElectric FieldElectric Field, cont.Slide 12Direction of Electric FieldDirection of Electric Field, contElectric Field LinesElectric Field Lines, cont.Electric Field Line PatternsSlide 18Slide 19Four point charges, each of the same magnitude, with varying signs are arranged at the corners of a square as shown. Which of the arrows labeled A, B, C, and D gives the correct direction of the net force that acts on the charge at the upper right corner?a Ab. Bc. Cd. De. The net force on that charge is zeroAnswer: bQuestion:QuestionObject A has a charge of +2 µC, and object B has a charge of +6 µC. Which statement is true:(a) FAB = –3FBA, (b) FAB = –FBA, or (c) 3FAB = –FBA Answer (b)e=×19C1.60 10 Q = ne (n =±0 、 1 、 2 、 3…)Electric charge always occurs in multiples of eA conducting sphere has a net charge of -4.8x10-17 C. What is the approximate number of excess electrons on the sphere?(a) 100 (c) 300 (e) 500(b) 200 (d) 400Answer: c (-4.8x10-17 C/-1.6x10-19 C=300 electrons)Question:Question:Two charges of +Q are 1 cm apart. If one of the charges is replaced by a charge of –Q, the magnitude of the force between them is (a) zero(b) smaller(c) the same (d) largerAnswer: cQuestion: A charge of +q is placed 2 cm from a charge of –Q. A second charge of +q is then placed next to the first. The force on the charge of –Q(a) decreases to half its former magnitude (b) remains the same (c) increases to twice its former magnitude(d) increases to four times its former magnitudeAnswer: cTwo positive point charges Q and 2Q are separated by a distance R. If the charge Q experiences a force of magnitude F when the separation is R, what is the magnitude of the force on the charge 2Q when the separation is 2R ?(a) F/4 (c) F (e) 4F(b) F/2 (d) 2FQuestion:Answer: aQuestion: Two charges, one positive and the other negative, are initially 2 cm apart and are then pulled away from each other until they are 6 cm apart. The force between them is now smaller by a factor of (a) 9(b) 3(c) 27(d) 3Answer: a•Electric Field •Electric Field LinesOutline for TodayElectric Field•Maxwell developed an approach to discussing fields•An electric field is said to exist in the region of space around a charged object–When another charged object enters this electric field, the field exerts a force on the second charged objectElectric Field, cont.•A charged particle, with charge Q, produces an electric field in the region of space around it•A small test charge, qo, placed in the field, will experience a forceElectric Field•Mathematically,•Use this for the magnitude of the field•The electric field is a vector quantity•The direction of the field is defined to be the direction of the electric force that would be exerted on a small positive test charge placed at that point2eorQkqFE Direction of Electric Field•The electric field produced by a negative charge is directed toward the charge–A positive test charge would be attracted to the negative source chargeDirection of Electric Field, cont•The electric field produced by a positive charge is directed away from the charge–A positive test charge would be repelled from the positive source chargeElectric Field Lines•A convenient aid for visualizing electric field patterns is to draw lines pointing in the direction of the field vector at any point•These are called electric field lines and were introduced by Michael FaradayElectric Field Lines, cont.•The field lines are related to the field by–The electric field vector, E, is tangent to the electric field lines at each point–The number of lines per unit area through a surface perpendicular to the lines is proportional to the strength of the electric field in a given regionElectric Field Line Patterns•Point charge•The lines radiate equally in all directions•For a positive source charge, the lines will radiate outwardElectric Field Line Patterns•For a negative source charge, the lines will point inwardElectric Field Line Patterns•An electric dipole consists of two equal and opposite charges•The high density of lines between the charges indicates the strong electric field in this
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