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Announcements

Announcements. Homework for tomorrow… (Ch. 32 , Probs . 36, 39, & 72 ) 32.16: a) 3.1 x 10 -4 Am 2 b) 5.0 x 10 -7 T 32.18 : a) 6.2 x 10 -7 T b) 1.8 x 10 9 A 32.27: a) (8.0 x 10 -13 N) jhat b) -(5.7 x 10 -13 N) jhat - ( 5.7 x 10 -13 N) khat Office hours…

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Announcements

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  1. Announcements • Homework for tomorrow… (Ch. 32, Probs. 36, 39, & 72) 32.16: a) 3.1 x 10-4 Am2 b) 5.0 x 10-7 T 32.18: a) 6.2 x 10-7 T b) 1.8 x 109 A 32.27: a) (8.0 x 10-13 N) jhat b) -(5.7 x 10-13 N) jhat - (5.7 x 10-13 N) khat • Office hours… MW 12:30-1:30 pm TR 9-10 am F 10-11 am • Tutorial Learning Center (TLC) hours: M 8-1 pm, 3-6 pm, W 8-1 pm, 2-6 pm TR 8-6 pm, F 8-2 pm

  2. Chapter 32 The Magnetic Field (Magnetic Forces on Current-Carrying Wires & Forces and Torques on Current Loops)

  3. Review… • The radius and frequency for cyclotron motion… • The force on a current-carrying wire in a B-field is…

  4. i.e. 32.14A current balance Two stiff, 50 cm long parallel wires are connected at the ends by metal springs. Each spring has an unstretched length of 5.0 cm and a spring constant of 0.025 N/m. The wires push each other apart when a current travels around the loop. How much current is required to stretch the springs to lengths of 6.0 cm.

  5. 32.9Forces and Torques on Current Loops Alternative but equivalent ways to view magnetic forces between two current loops. Parallel currents attract, opposite currents repel. Opposite poles attract, like poles repel.

  6. 32.9Forces and Torques on Current Loops Consider a current loop in a B-field… • Ffront and Fback are opposite in direction, but equal in magnitude, therefore ΣFx=0. • Ftopand Fbottomare opposite in direction, but equal in magnitude, therefore ΣFy=0. • Ftop and Fbottomexert a net torque, therefore Στ≠0! So what is the net torque?

  7. 32.9Forces and Torques on Current Loops Consider a current loop in a B-field… • Ffront and Fback are opposite in direction, but equal in magnitude, therefore ΣFx=0. • Ftopand Fbottomare opposite in direction, but equal in magnitude, therefore ΣFy=0. • Ftop and Fbottomexert a net torque, therefore Στ≠0! So what is the net torque?

  8. Quiz Question 1 If released from rest, the current loop will • Move upward. • Move downward. • Rotate clockwise. • Rotate counterclockwise. • Do something not listed here.

  9. 32.9Forces and Torques on Current Loops A simple electric motor…

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