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The second midterm exam for the electrodynamics course (physics 323) held in spring 2004. The exam consists of 12 questions and covers topics such as vector potential, electric fields, charged spheres, and radio antennas. Students are required to write their name, id, and calculations on the question sheets. The exam lasts for 60 minutes and is closed-book with no notes or calculators allowed.
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Electrodynamics, Physics 323 Second midterm 8.20 am, May 19, 2004 Spring 2004 Instructor: David Cobden
You have 60 minutes. End on the buzzer at 9.20. Answer all 12 questions.
Write your name on every page and your ID on the first page.
Write all your working on these question sheets. Use this cover page for extra working (you might get credit for it.)
It is important to show your calculation or derivation. You may not get full marks just for stating the correct answer if you don’t show how you get it.
Watch the blackboard for corrections or clarifications during the exam.
This is a closed book exam. No notes allowed. No calculators.
c = 3 × 10^8 m/s.
Don’t turn this page until I say ‘go’.
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I. 1. [6] The vector potential sometimes obeys the following equation: W 2 A x ( , ) t = − μ 0 J x ( , ) t.
Write W^2 explicitly in terms of derivatives. What is the condition for this equation to be valid?
III. A radio station has an antenna on top of Queen Anne Hill which is a vertical wire. It emits a power of 100 kW at 90 MHz.
2 0 6
p P c
μ π
, or
otherwise, estimate roughly the average current I flowing in the antenna.