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Announcements. Homework for tomorrow… (Ch . 26 CQs 8, Probs. 13 & 15) 25.62: E 1 = (4.0 x 10 4 N/C) ihat + (8.0 x 10 4 N/C ) jhat , E 2 = ( 4.5 x 10 5 N/C ) ihat , E 3 = (4.0 x 10 4 N/C) ihat - (8.0 x 10 4 N/C) jhat 26.3: E = 1.1 x 10 4 N/C, 10° below x -axis
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Announcements • Homework for tomorrow… (Ch. 26 CQs 8, Probs. 13 & 15) 25.62: E1 = (4.0 x 104 N/C) ihat + (8.0 x 104 N/C) jhat, E2= (4.5 x 105 N/C) ihat, E3 = (4.0 x 104 N/C) ihat- (8.0 x 104 N/C) jhat 26.3: E = 1.1 x 104 N/C, 10° below x-axis 26.5: E = (36 N/C) ihat at (0.10 , 0) m, E = -(18 N/C) ihat at (0 , 0.10) m • Office hours… MW 12:30-1:30 pm TR 9-10 am F 10-11 am • Tutorial Learning Center (TLC) hours: M 8-1 pm, 3-6 pm, W 8-1 pm, 2-6 pm TR 8-6 pm, F 8-2 pm
Chapter 26 The Electric Field (The E-Fields of Rings, Disks, & Planes)
Last time… • Linear & surface charge densities • E-field of a rod of length L & charge Q in the bisecting plane.. • E-field of an infinite line charge.. + + + + + + + + + + + + + + + + + + + r L P
Quiz Question 1 Two protons, A and B, are in an E-field. Which proton has the larger acceleration? • Proton A • Proton B • Both protons have the same acceleration
i.e. 26.4E-field of a ring of charge.. A thin ring of radius R is uniformly charged with total charge Q. Find the E-field at a point on the axis of the ring (perpendicular to the ring).
i.e. 26.4E-field of a ring of charge.. A thin ring of radius R is uniformly charged with total charge Q. Find the E-field at a point on the axis of the ring (perpendicular to the ring). • Q: What about for –z? • Q: What about for –Q?
Quiz Question 2 Positive charge +Q is uniformly distributed on the upper half of a semicircular rod and negative charge –Q is uniformly distributed on the lower half. What is the direction of the electric field at point P, the center of the semicircle? • Up. • Down. • Left. • Right. • Up and to the left. +Q P -Q
E-field of a disk of charge.. A disk of radius R is uniformly charged with total charge Q. Find the electric field at a point on the axis of the disk (perpendicular to the disk).
E-field of a disk of charge.. A disk of radius R is uniformly charged with total charge Q. Find the electric field at a point on the axis of the disk (perpendicular to the disk). Notice: • For z<0, same magnitude but opposite direction
E-field of a plane of charge.. A planeis uniformly charged with uniform surface charge density η. Find the E-field… + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + ∞ ∞
E-field of a plane of charge.. A planeis uniformly charged with uniform surface charge density η. Find the E-field… + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + ∞ ∞ Notice: • A constant! • Zero height dependence?
Quiz Question 3 Two protons, A and B, are next to an infinite plane of positive charge. Proton B is twice as far from the plane as proton A. Which proton has the larger acceleration? • Proton A. • Proton B. • Both protons have the same acceleration.
E-field of a sphere.. A sphere of charge Q and radius R (uniformly charged or a spherical shell) has an E-fieldof the form… • Exactly the same as that of a point charge!