Discussion
The de Broglie wavelength of an electron travelling with 1% speed of light is about :
(mass of electron and speed of light are 9.109 × 10−31 kg and 2.998 × 108 ms−1 respectively) :
Answer: D
The wavelength is about 243 pm.
The speed is 1% of c, so v = 2.998 × 106 m s−1, which is slow enough to ignore relativity. Then
\[ \begin{aligned} \lambda &= \frac{h}{mv} \\ &= \frac{6.626 \times 10^{-34}}{9.109 \times 10^{-31} \times 2.998 \times 10^{6}} \\ &= 2.43 \times 10^{-10}\ \text{m} = 243\ \text{pm} \end{aligned} \]
The other options keep the digits 243 but attach the wrong unit; 243 Å would be 2.43 × 10−8 m, a hundred times too long.
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