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Announcements

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

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Announcements

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  1. Announcements • Homework for tomorrow… (Ch. 26, Probs. 22 & 50) CQ 8: 2nC/cm2 26.12: a) 0 b) –(4.1 x 103 N/C)ihat 26.42: Lim_{z<<R} -> KQz/R3 , Lim_{z>>R} -> KQ/z2 • 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. Last time… • E-field of a infiniteplane of charge.. • E-field of a sphere (of radius R) of charge.. • E-field of a parallel-plate capacitor..

  4. 26.7: Motion of a Dipole in an E-field Recall the polarization force between a q’ed & neutral object… • The qpolarizes 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. - - - - - - - + - - + - - - + - - + - + - - + +

  5. Motion of a Dipole in an E-field 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… + -

  6. Motion of a Dipole in an E-field 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… + -

  7. Motion of a Dipole in an E-field Consider a dipole in a non-uniform electric field… Notice: • The dipole 1st 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.

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

  9. i.e. 26.11: The force on a H2O molecule. H2O 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 H2O molecule?

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