To find the smallest (minimum) wavelength of X-rays made by 20 kV electrons, use this formula: ‌λmin=‌
hc
E
=‌
hc
eV
‌ where: ‌ ‌h=‌ Planck's constant ‌=6.626×10−34Js ‌c=‌ speed of light ‌=3×108m∕s ‌e=‌ charge of electron ‌=1.6×10−19C ‌V=‌ voltage ‌=20,000V=20×103V Plug in the numbers: λ‌min ‌=‌
6.626×10−34×3×108
1.6×10−19×20×103
Solve the calculation: λmin=0.062×10−9m We can also write this as: λmin=0.062nm