Physics 272: Advanced Honors Physics II
due in class Monday, February 26, 2018
Reading: Purcell 4.7-9
the solution for each problem and your name should be
written on a separate page (sorry, trees!) to facilitate
the grading. Please paperclip the pages together.
I have put the answers (or in some cases partial
answers) at the bottom of this page. You can use them to
check your own answers -- if they don't agree, you know
you need to go back and look for at least one mistake.
4.21(a) Current pulse from an alpha particle: planar
The current flows in the circuit to transport negative
charge from the surface of the left-hand conducting
plate to the surface of the right-hand conducting plate
as the positively charged particle moves to the right
(the charges on the plates can be found from the
superposition argument in Exercise 3.37. You just need
the answer: the total charge on the surface of the
left-hand plate Q1 = -(s-x) Q/s and the total charge on
the right-hand plate Q2 = -Q-Q1=-Qx/s, where s is the
separation between the plates and x is the perpendicular
distance from Q to the left-hand plate. Here's the derivation
of the answer if you are interested).
Note that this is NOT a steady current system as the
charge distribution is changing with time.
2. 4.38 Two light bulbs *
3. 4.39 Maximum power *
If you are unfamiliar with the concept of internal
resistance of a battery, look at Figure 4.21 on p. 211
and corresponding short discussion at the bottom of p.
210 of Purcell. If you need more words, check out the discussion
4. 4.40 Minimum power dissipation **
OPTIONAL **4.21(b) Current
pulse from an alpha particle: cylindrical
As part of the solution, you have to
generalize the superposition argument in
Exercise 3.37 to concentric cylinders.
4.21(a) 1.6 x
4.38. (a) 2 is larger; (b) 2 is brighter