In the spectrum of single ionised helium, the wavelength of a line observed is almost the same as the first line of Balmer series of hydrogen. It is due to transition of electron from
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In the spectrum of single ionised helium, the wavelength of a line observed is almost the same as the first line of Balmer series of hydrogen. It is due to transition of electron from

G1 Physics · Accepted Answer

Step 1: For a hydrogen-like atom, Eₙ = −13.6Z²/n² eV and photon energy is ΔE = 13.6Z²|1/n₂²−1/n₁²| = hc/λ. Step 2: Use the stated transition/excitation condition to obtain the required value. Final: A: n₁ = 6 to n₂ = 4.