# NEET Questions Solved

NEET - 2011

Electrons used in an electron microscope are accelerated by a voltage of 25 kV. If the voltage is increased to 100 kV then the de-Broglie wavelength associated with the electrons would

(a) decrease by 2 times

(b) decrease by 4 times

(c) increase by 4 times

(d) increase by 2 times

We have

$\mathrm{\lambda }=\frac{12.27}{\sqrt{\mathrm{V}}}$

So,        $\frac{{\mathrm{\lambda }}_{1}}{{\mathrm{\lambda }}_{2}}=\sqrt{\frac{{\mathrm{V}}_{2}}{{\mathrm{V}}_{1}}}\phantom{\rule{0ex}{0ex}}{\mathrm{\lambda }}_{2}={\mathrm{\lambda }}_{1}\sqrt{\frac{{\mathrm{V}}_{1}}{{\mathrm{V}}_{2}}}\phantom{\rule{0ex}{0ex}}{\mathrm{\lambda }}_{2}={\mathrm{\lambda }}_{1}\sqrt{\frac{25}{100}}\phantom{\rule{0ex}{0ex}}{\mathrm{\lambda }}_{2}={\mathrm{\lambda }}_{1}\sqrt{\frac{1}{4}}=\frac{{\mathrm{\lambda }}_{1}}{2}$

Difficulty Level:

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