Select the option(s) in which the velocity of electron is greater than $1.3 \times 10^{6} m/sec$ . {hc=1240 eV.nm}

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The electron which is accelerated from rest position by a potential 45.5 V

An electron moving in the first Bohr orbit of $H e^{+}$

The electron having deBroglie wavelength of $4 π \times 0.526 \overset{o}{A}$ .

The electron with maximum kinetic energy emitted from a metal whose threshold wavelength is 400 nm and is subjected to electromagnetic radiations having wavelength 124 nm.

answer is A, B, D.

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Detailed Solution

A) $\frac{1}{2} m ν^{2} = q . V ν = 4 \times 10^{6} m/sec$

(B) $ν = \frac{2 π K Z e^{2}}{n h} ν = 4.38 \times 10^{6} m / \sec$

(C) $λ = \frac{h}{m ν} ν = 1.09 \times 10^{6} m/sec$

(D) ${[K . E]}_{\max} = \frac{h c}{λ} - \frac{h c}{λ_{0}} {[K . E]}_{\max} = \frac{1}{2} m ν^{2} ν = 1.55 \times 10^{6} m/sec$