Negative…

Small charge Charge density Small length Small area Small volume

All charged rods have the same length and the same linear charge density (+ or -). Light rods are positively charged, and dark rods are negatively charged. For which arrangement below would the magnitude of the electric field at the origin be largest? Impossible to determine

Where does the negatively charged triangle go?

Rules for Sketching 1.Lines begin on positive charges and terminate on negative charges – If more of one type of charge, some lines will begin or end infinitely far away. 2.The number of lines leaving a positive charge or approaching a negative charge is proportional to the magnitude of the charge. 3.No two field lines can cross.

May be helpful as you practice this: u/sims/charges-and- fields/charges-and- fields_en.html

Two uniformly charged rods are positioned horizontally as shown. The top rod is positively charged and the bottom rod is negatively charged. The total electric field at the origin: 1.is zero. 2.has both a non-zero x component and a non-zero y component. 3.points totally in the +x direction. 4.points totally in the –x direction. 5.points totally in the +y direction 6.points totally in the –y direction. 7.points in a direction impossible to determine without doing a lot of math.

Rank the magnitudes of the electric field at points A, B, and C shown in the figure(greatest magnitude first). 1. A, B, C 2. C, A, B 3. B, C, A 4. C, B, A 5. A, C, B 6. B, A, C

Example: A uniformly charged rod of length L and total charge Q lies along the x axis as shown in the figure. (a) Find the components of the electric field at the point P on the y axis a distance d from the origin. (b) What are the approximate values of the field components when d >> L? Explain why you would expect these results. x y P d L

Quantitative Question: You are helping to design a new electron microscope to investigate the structure of the HIV virus. A new device to position the electron beam consists of a charged circle of conductor. This circle is divided into two half circles separated by a thin insulator so that half of the circle can be charged positively and half can be charged negatively. The electron beam will go through the center of the circle. To complete the design your job is to calculate the electric field in the center of the circle as a function of the amount of positive charge on the half circle, the amount of negative charge on the half circle, and the radius of the circle.

Lab: None Start on homework: P37, P42, P43, P46 from Chapter 23