Question

Energy associated with the first orbit of $He^+$ is

• A. $ 8.72 \times 10^{-18} \, joules $
• B. $ 0.872 \times 10^{-18} \, joules $
• C. $ -0.872 \times 10^{-18} \, joules $
• D. $ -8.72 \times 10^{-18} \, joules $

Answer 1

Answer: (D)

For H-like particles,
$E_n = \frac{-21.78 \times 10^{-19}}{n^2} Z^2 \, J$
$= \frac{-21.78 \times10^{-19}}{1^{2}} \times\left(2\right)^{2} = - 8.712 \times10^{-18 }J$