Question

An electron is moving with a kinetic energy of 4.55 $\times 10^{- 25}$ J. The de Broglie wavelength for it is
(Given: $\text{h} = 6.626 \times 10^{- 34} , \, \text{m}_{\text{e}} = 9.1 \times 10^{- 31} \, \text{kg}$ )

• A. $7.2\times 10^{- 7}m$
• B. $72\times 10^{- 7}m$
• C. $0.72\times 10^{- 7}m$
• D. $4.2\times 10^{- 7}m$

Answer 1

Answer: (A)

$\text{K} \text{.E} \text{.} = \frac{1}{2} \, \text{mv}^{\text{2}}$
$V=\sqrt{\frac{2 K E}{m}}$
$=\sqrt{\frac{2 \times 4.55 \times 1 0^{- 25}}{9.1 \times 1 0^{- 31} k g}}$
$= 10^{3} \, \text{mS}^{- 1}$
$\lambda =\frac{h}{m v}=\frac{6.626 \times 1 0^{- 34}}{9.1 \times 1 0^{- 31} \times 1 0^{3}}$
$= 7.2 \times 10^{- 7} \, \text{m}$