Question
Question: An electron has a total energy of 2 MeV. Calculate the effective mass of the electron in kg and its ...
An electron has a total energy of 2 MeV. Calculate the effective mass of the electron in kg and its speed. Assume rest mass of electron 0.511 MeV.
A
2.9×108
B
8.01×108
C
9.652×108
D
None
Answer
2.9×108
Explanation
Solution
Mass of electron in motion =9312amu (1 amu = 931 MeV)
=9312×1.66×10−27kg=3.56×10−30kg (1)
amu=1.66×10−27kg)
Let the speed of the electron be u.
m′=1−(u/c)2m or
3.56×10−30=1−(3×108u)29310.511×1.66×10−27=1−(3×108u)20.911×10−30or 1−(3×108u)2=0.06548 or u2=9×1016×0.93452 or u=2.9×108m