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Question

If the energy of an electron in the second orbit of hydrogen is −3.4 eV, what is the energy in the fourth orbit?

This question was previously asked in
RRB ALP 2025 CBT 2 Wiremen Question Paper (28-Jul-2026) (Shift 2)
The correct answer is
−0.85 eV

Hydrogen Electron Energy Calculation

The energy of an electron in a hydrogen atom is determined by its principal quantum number, n. The energy levels follow the formula:

\(E_n = \frac{E_1}{n^2}\)

where E1 is the ground state energy (−13.6 eV) and n is the orbit number.

Alternatively, the energy of an electron in orbit n can be related to its energy in orbit m using the ratio:

\(E_n = E_m \times \frac{m^2}{n^2}\)

Step-by-Step Calculation

  1. Identify the given values:

    • Energy in the second orbit (\(n=2\)): \(E_2 = -3.4\) eV.
    • We need to find the energy in the fourth orbit (\(n=4\)).
  2. Apply the energy ratio formula:

    \(E_4 = E_2 \times \frac{2^2}{4^2}\)

  3. Substitute the known values:

    \(E_4 = -3.4 \text{ eV} \times \frac{4}{16}\)

  4. Simplify the expression:

    \(E_4 = -3.4 \text{ eV} \times \frac{1}{4}\)

  5. Calculate the final energy:

    \(E_4 = -0.85 \text{ eV}\)

The energy of the electron in the fourth orbit is −0.85 eV.

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