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Published byScarlett Harrison Modified over 4 years ago

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**Announcements Homework for tomorrow… Ch. 32: Probs. 37, 39, & 48**

CQ6: a) up b) left 32.16: a) 3.1 x 10-4 Am2 b) 5.0 x 10-7 T 32.50: 3,200 Office hours… MW 12:30-1:30 pm TR am F 1-2 pm Tutorial Learning Center (TLC) hours: MW 8-10 am, 12-6 pm R 8-12 pm, 2-6 pm T 8-1 pm, 2-6 pm F 8-10 am, 2-5 pm

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**Chapter 32 The Magnetic Field**

(Magnetic Forces on Current-Carrying Wires & Forces and Torques on Current Loops)

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**Review… The radius and frequency for cyclotron motion…**

The force on a current-carrying wire in a B-field is…

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Quiz Question 1 The horizontal wire can be levitated – held up against the force of gravity – if the current in the wire is Right to left. Left to right. It can’t be done with this magnetic field.

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**Force Between Two Parallel Wires**

What is the force on wire1 due to wire2?

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**Force Between Two Parallel Wires**

What is the force on wire1 due to wire2?

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i.e A 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 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.

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**32.9 Forces 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.

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**32.9 Forces 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. Ftop and Fbottom are opposite in direction, but equal in magnitude, therefore ΣFy=0. Ftop and Fbottom exert a net torque, therefore Στ≠0! So what is the net torque?

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**32.9 Forces 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. Ftop and Fbottom are opposite in direction, but equal in magnitude, therefore ΣFy=0. Ftop and Fbottom exert a net torque, therefore Στ≠0! So what is the net torque?

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**Quiz Question 2 If released from rest, the current loop will**

Move upward. Move downward. Rotate clockwise. Rotate counterclockwise. Do something not listed here.

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**32.9 Forces and Torques on Current Loops**

A simple electric motor…

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