The speed of an electron in the n = 3 orbit of He + is compared with that of an electron in the n = 2 orbit of hydrogen. What is the ratio v He+ /v H ?

⚛️ Physics · Atoms · NEET & JEE

The speed of an electron in the n = 3 orbit of He+ is compared with that of an electron in the n = 2 orbit of hydrogen. What is the ratio vHe+/vH?

Answer: 4/3.

A 2/3
B 4/3
C 1
D 3/2

Correct answer: B. 4/3

Explanation: For a hydrogen-like atom, v is proportional to Z/n. Thus the ratio is (2/3)/(1/2) = 4/3.

Comparison of the Thomson model and the Rutherford model of the atom: in the Thomson plum pudding model alpha particles pass almost straight through a diffuse positive sphere, while in the Rutherford model a concentrated central nucleus deflects some alpha particles through large angles, with the lower panels showing the alpha particle source and gold foil and the observed result of wide-angle scattering

The Geiger–Marsden alpha-scattering result: a few alpha particles bounce back at large angles, which rules out Thomson’s diffuse model and demands a tiny, massive, positively charged nucleus. Image: Kurzon, CC BY 3.0, via Wikimedia Commons.

Concept context

Thomson's plum-pudding model, Rutherford's nuclear model from alpha-scattering, Bohr's postulates and hydrogen spectrum, spectral series (Lyman to Pfund), Rydberg formula, and limitations of each model.

Read the full Atoms notes →

The speed of an electron in the n = 3 orbit of He<sup>+</sup> is compared with that of an electron in the n = 2 orbit of hydrogen. What is the ratio v<sub>He+</sub>/v<sub>H</sub>?

Concept context

More Atoms questions