Understanding Electric Fields and Dipole Motion in Chapter 26 of Physics
This announcement covers key concepts in Chapter 26 of the physics course, focusing on electric fields and the motion of dipoles within them. Topics include the electric field of an infinite plane of charge, a sphere of charge, and the behavior of dipoles in uniform and non-uniform electric fields. Important equations such as the polarization force and induced dipole moments are discussed. Additionally, office hours and tutorial center timings are provided for student support. Homework problems related to these concepts are due tomorrow.
Understanding Electric Fields and Dipole Motion in Chapter 26 of Physics
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Presentation Transcript
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
Chapter 26 The Electric Field (Motion of a dipole in an E-field)
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..
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. - - - - - - - + - - + - - - + - - + - + - - + +
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… + -
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… + -
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.
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.
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?