An electron microscope uses electrons of $40 \ keV$. The de Broglie wavelength associated with these electrons is approximately:

$A$ ball of mass $0.12 \ kg$ is moving with a speed $20 \ m \ s^{-1}$. Then its de Broglie wavelength is . . . . . . . ( $h = 6.63 \times 10^{-34} \ J \ s$ )

An electron beam is incident on a crystal. The interplanar spacing of the crystal is $b$. Which of the following de Broglie wavelengths of the electron beam will result in direct reflection?

$A$ photon and an electron (mass $m$) have the same energy $E$. The ratio $\left(\frac{\lambda_{\text{photon}}}{\lambda_{\text{electron}}}\right)$ of their de Broglie wavelengths is: ($c$ is the speed of light)

If the linear momentum of a proton is changed by $p_0$,then the de Broglie wavelength associated with the proton changes by $0.25 \%$. Then the initial linear momentum of the proton is

An $\alpha$ particle and a proton are accelerated from rest by a potential difference of $200 \ V$. After this,their de Broglie wavelengths are $\lambda_{\alpha}$ and $\lambda_{p}$ respectively. The ratio $\frac{\lambda_{p}}{\lambda_{\alpha}}$ is