Q. Two large parallel plates are connected with the terminal of $100\ v$ power supply. These plates have a fine hole at the centre. An electron having energy $200\ eV$ is so directed that it passes through the holes. When if comes out it’s de-Broglie wavelength is
A) $1.22\ \mathring{\mathrm{A}}$
B) $1.75\ \mathring{\mathrm{A}}$
C) $2\ \mathring{\mathrm{A}}$
D) None of these
Explanation
(a) Energy of the electron, when it comes out from the second plate $= 200\ eV - 100\ eV = 100\ eV$
Hence accelerating potential difference $= 100\ V$
$\lambda_{Electron} = \frac{12.27}{\sqrt{V}} = \frac{12.27}{\sqrt{100}} = 1.23\mathring{\mathrm{A}}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.