Question

Two large parallel plates are connected with the terminal of $100V$ power supply. These plates have a fine hole at the centre. An electron having energy $200eV$ is so directed that it passes through the holes. When it comes out it's de-Broglie wavelength is

• A. $1.22A^{\circ }$
• B. $1.75A^{\circ }$
• C. $2A^{\circ }$
• D. none of these

Answer 1

The correct option is A $1.22A^{\circ }$

Energy of the electron, when it comes out from the second plate $=200eV-100eV=100eV$

Hence acceleration potential difference $=100V$

${\lambda }_{Electron}=\frac{12.27}{\sqrt{V}}=\frac{12.27}{\sqrt{100}}=1.23\stackrel{o}{A}$