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Asked in GUJCET 2025 · Postulates, radius, speed and angular momentum
Given: h=6.63×10⁻³⁴ J s. Counting the ground state as n=1, the first excited state is n=2, so the third excited state is n=4.
Idea: Bohr's second postulate lets the electron carry only whole multiples of h/(2π) of orbital angular momentum, L=(nh)/(2π).
L=(4×6.63×10⁻³⁴)/(2π)=(2×6.63×10⁻³⁴)/(3.14).
L=4.22×10⁻³⁴ J s.
A joule second is a kg m² s⁻¹, so this is the 4.2×10⁻³⁴ kg m² s⁻¹ of the first option.
Beware the labelling: third excited state means n=4, not n=3.
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