Consider the figure given below. Suppose the voltage applied to A is increased. The diffracted beam will
have the maxima at a value of $\theta$ that [NCERT Exemplar]

In Davisson - Germer experiment, the de-Broglie wavelength associated with electron,

$\lambda =\frac{12.27}{\sqrt{V}} \stackrel{0}{\mathrm{A}}$              …(i)

where, V is the applied voltage.

If there is a maxima of the diffracted electrons at an angle $\theta$, then

$2d\sin \theta =\lambda$        …(ii)

From Eq. (i), we note that if V is inversely proportional to the wavelength $\lambda .$

i.e. V will increase with the decrease in the $\lambda .$

From Eq. (ii), we note that, wavelength $\lambda$ is directly proportional to sin $\theta$ and hence $\theta$.

So, with the decrease in $\lambda ,$ $\theta$ will also decrease.

Thus, when the voltage applied to A is increased. The diffracted beam will have the maxima at a value of $\theta$ that will be less than the earlier value.