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How do i do this wavelength question?
There are electron sources of 10kV, 20kV and 30kV. What is the minimum wavelength radiation emitted by the 20kV source.
Can someone please show me how to work this out? thanks.
1 Answer
- CingcangkelingLv 77 years ago
Electron in potential difference V have potential energi
PE = q V...........
q =electric charge = 1,6×10^-19 C
The potential energy then convert to kinetic energi
KE = ½ m v²
m = electron mass = 9,1×10^-31 kg
From the conservation of energi
KE = PE
½ m v² = q V
........v² = 2qV/m
.........v = √(2qV/m)
de-Broglie wave length
.......h
λ = ------
......m v
.......h
...= --------------------
......m √(2qV/m)
.......h
...= --------------
......√(2qmV)
for V = 20 kV = 2×10^5 V, the wave length
.......h
λ.= --------------
......√(2qmV)
.......6,6×10^-34 Js
...= --------------------------------------------------------------------
......√(2 (1,6×10^-19 C) (9,1×10^-31 kg) (2×10^5 V)
...= 2.73×10^-12 m..<-- answers
Ok ?
