1. Announcements  Homework for tomorrow… (Ch. 26, Probs. 22 & 50) CQ 8: 2nC/cm 2 26.12: a) 0b) –(4.1 x 10 3 N/C)ihat 26.42: Lim_{z KQz/R 3, Lim_{z>>R} -> KQ/z 2  Office hours… MTWRF 9-10 am  Tutorial Learning Center (TLC) hours: MW 8-5 pm T 8-6 pm R 8-11 am, 2-5 pm F 8-2 pm

2. Chapter 26 The Electric Field (Motion of a dipole in an E-field)

3.  E-field of a infinite plane of charge..  E-field of a sphere (of radius R) of charge..  E-field of a parallel-plate capacitor.. Last time…

4. Recall the polarization force between a q’ed & neutral object…  The q polarizes the neutral object, creating an induced electric dipole.  The q then exerts an attractive force on the near end of the dipole that is slightly stronger than the repulsive force on the far end. 26.7: Motion of a Dipole in an E-field - - - - - - - - - - - - - + + + ++ + + - - - -

5. Consider a dipole in a uniform electric field… Notice:  There is NO net force on a dipole in a uniform E-field.  The dipole experiences a torque… Motion of a Dipole in an E-field + -

6. Consider a dipole in a uniform electric field… Notice:  There is NO net force on a dipole in a uniform E-field.  The dipole experiences a torque… Motion of a Dipole in an E-field + -

7. Consider a dipole in a non-uniform electric field… Notice:  The dipole 1 st rotates until aligned with the E-field.  The net force on a dipole is toward the direction of the strongest field. A dipole will experience a net force toward any charged object. Motion of a Dipole in an E-field

8. An electrically neutral dipole is placed in an external field. In which situation(s) is the net force on the dipole zero? 1. (a) 2. (c) 3. (b) and (d) 4. (a) and (c) 5. (c) and (d) 6. Some other combination. Quiz Question 1

9. H 2 O has a permanent dipole moment of magnitude 6.2 x 10 -30 Cm. A water molecule is located 10 nm from a Na + ion in a saltwater solution. What force does the ion exert on the H 2 O molecule? i.e. 26.11: The force on a H 2 O molecule.