Imagine that you have a larger version of the apparatus you will use in this lab
ID: 1424239 • Letter: I
Question
Imagine that you have a larger version of the apparatus you will use in this lab. However, your Helmholtz coils are broken, so you decide to try using the Earth's magnetic field instead. To accomplish this, you align the system such that the Earth's field passes through the device in the same direction as the field from the Helmholtz coils would have. How large would be the radius of the ensuing electron ring? At this latitude, the magnitude of the Earth's field is about 5.1 x 10-5 Tesla. For the accelerating voltage, use V = 200 Volts.
meters
Explanation / Answer
mass of electron m = 9.11 x 10-31 kg
charge on electron = e = 1.6 x 10-19 C
potential difference V = 200 V
Kinetic energy = (1/2) mv2 = eV
mv = (2meV)1/2
radius of circular orbit in a magnetic field , R = mv / eB
R = (2meV)1/2 / eB = 0.936 m