What voltage must be applied to an elect-non microscope to produce electrons of wavelength `0.4A`?

Explanation

To find the voltage that must be applied to an electron microscope to produce electrons of wavelength \(0.4 \, \text{Å}\), we can use the de Broglie wavelength formula. Here’s a step-by-step solution:

### Step 1: Write down the de Broglie wavelength formula
The de Broglie wavelength \(\lambda\) of a particle is given by the formula:
\[ \lambda = \frac{h}{\sqrt{2m e V}} \]
where:
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