# Homework Set #13 ```PHY 2020
Homework Set #13
Fall 2014
Name:
Due: At the start of class on Wednesday, Dec. 3. Not 5 minutes after the start of class.
If you just give an answer without showing how you arrived at that answer, then you will
get no credit for the problem.
Here are some facts:
The mass of an electron is 9 &times; 10−31 kg.
The electric charge of an electron is −1.6 &times; 10−19 Coulombs
unit of magnetic field: Tesla
Here are some of the formulae that you will be given on the tests coming up.
~ : F = qvB
force on a charge moving in a magnetic field when ~v ⊥B
~ :F =0
force on a charge moving in a magnetic field when ~v k B
sound in air: λf = vsound = 340 m/s
organ pipe, one end open: λ = 4L/(1 + 2n) where n is an integer starting at 0
sound femitted
Doppler effect, approaching source fheard = vvsound
−vsource
sound femitted
Doppler effect, receding source fheard = vvsound
+vsource
1. (1pt) An electron is moving in a circle in a magnetic field and has a constant speed of
1.0 &times; 105 m/s and a radius R = 1 cm.
(a) What is the magnitude of the acceleration of the electron?
(b) What is the magnitude of the magnetic field?
2. (1pt) An organ pipe has a length of 2m
(a) What is the wavelength of sound for the lowest note that this pipe can make?
(b) What is the frequency of this lowest note?
(c) What is the wavelength of the note for n = 2?
(d) And what is the frequency of the note for n = 2?
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