Electrons with de-Broglie wavelength λ fall on the target in an X-ray tube. The cut off wavelength of the emitted X-rays is
a. \lambda_0 = \frac{2mc\lambda^2}{h}
b. \lambda_0 = \frac{2h}{mc}
c. \lambda_0 = \frac{2m^2c^2\lambda^3}{h^2}
d. \lambda_0 = \lambda