IB Physics HL E 1 11 Hl Bohr Angular Momentum Questions

Apply HL Bohr angular-momentum quantization to electron orbits, relating radius, speed, stability and the condition mvr=nh/(2π).

Exam points

state and apply the Bohr angular-momentum condition mvr=nh/(2π) to identify allowed electron orbits
derive or calculate changes in orbital radius and electron speed between hydrogen energy levels
explain why quantized non-radiating orbits were introduced to stabilise the Rutherford model and interpret orbital-radius calculations

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Study E.1.11 (HL)—Bohr angular momentum conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

[Maximum number: 4]

(a)

Bohr modified the Rutherford model by introducing the condition $m v r=n \frac{h}{2 \pi}$ .

Outline the reason for this modification.

[ 3 ]

the electrons accelerate and so radiate energy;
they would therefore spiral into the nucleus/atoms would be unstable

electrons have discrete/only certain energy levels

the only orbits where electrons do not radiate are those that satisfy the Bohr condition $mvr=n\frac{h}{2\pi}$

(b)

Calculate the electron's orbital radius in (c)(ii).

[ 1 ]

$r=\frac{(6.63\times10^{-34})^2}{4\pi^2\times8.99\times10^9\times9.11\times10^{-31}\times(1.6\times10^{-19})^2} r=5.3\times10^{-11}\ \mathrm{m}$

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IB Physics HL E 1 11 Hl Bohr Angular Momentum Questions question 1

Question (a)

Question (b)