E-7

Because of the equipment difference, we are unable to get the result as manual described. The most diffcult thing is to measure r(the radius of the circular motion of the electrons). the result of the experiment is not so accurate as we expected. However, from the observation, we can understand the procedure, and the ratio of the mass to charge of the electron can be measured.

• 1. The precision of current is 20mA. The precision of voltage is 50V. The precision of R is 1mm(Because we can not directly measure R, the error may be greater.)
• 3. If the tube was not evacuated, the electrons would collide with the molecules of air, losing some kinetic energy. As a result, the elctrons couldn't reach the anode with the expected speed. The result of the experiment would be inacurrate.
• 4. We can obtain the values from the table of atomic constants as
  m = 9.tx10^-31kg,   q= 1.6x10^-19C.     therefore, use
  mv²/2 = qV,     we have
  (9.1x10^-31kg)v²/2 = (1.6x10^-19C)(100V)Þ v = 5.9x10⁶m/s