MIDTERM 1 UTC 4.132 Thu-Sep 27, 7:00PM - 9:00PM Bring pencils, calculators (memory cleared) Course Summary Unit 1 Provided
Question 1 Which one of these statements is true? When near the center of the object, the electric field hardly changes with increasing distance from a uniformly charged long rod. a uniformly charged ring. a uniformly charged disk. a point charge.
Question -Q +Q metal plastic A solid metal ball carrying negative excess charge is placed near a uniformly charged plastic ball. Which one of the following statements is true? The electric field inside both balls is zero. The electric field inside the metal ball is zero, but it is nonzero inside the plastic ball. The electric fields inside both objects are nonzero and are pointing toward each other. The electric field inside the plastic ball is zero, but it is nonzero inside the metal ball.
Review 1) Vector Arithmetic Find = <observation loc.> - <source loc.> 2) Electric Force and Field of a Charged Particle -Q
Review y 3) Dipoles -Q +Q x from – to + Electric field of a dipole Forces on a dipole Electric field due to something else. Calculate force on each Charge
Review 4) Induced Dipoles Know and gives – + Example: Force between charge and induced dipole
Review 4) Polarization of Metals and Insulators + + + + Metal Metal + + + + + Insulator + Insulator + + Neutral Excess + What is E inside metal in static equilibrium?
General Procedure for Calculating Electric Field of Distributed Charges • Cut the charge distribution into pieces for which the field is known • Write an expression for the electric field due to one piece • (i) Choose origin • (ii) Write an expression for DE and its components • Add up the contributions of all the pieces • (i) Try to integrate symbolically • (ii) If impossible – integrate numerically • Check the results: • (i) Direction • (ii) Units • (iii) Special cases
Review 6) Flux and Gauss’ Law Examples: Spherical Shell, Long Rod, Large Sheet
Review 6) Gauss’s Law and Metals Use E=0 inside metals Examples: Neutral Metal Solid with Void; Charge in Void 7) Superposition Example: Large Sheet and Infinite Rod X X X