IB Physics HL D.2.12 Two-charge potential energy Question Bank

Practise IB Physics HL D.2.12 by applying two-charge potential energy concepts to exam-style physics questions.

Exam points

identify the relevant physical quantity, model or diagram
apply the correct equation and units to the evidence
justify the result using conservation laws, fields or energy relationships

[Maximum number: 4]

(a)

In a classical model of the singly-ionized helium atom, a single electron orbits the nucleus in a circular orbit of radius r.

[ 4 ]

(i)

Hence, deduce that the total energy of the electron is given by $E_{\mathrm{TOT}}=-\frac{k e^{2}}{r}$ .

[ 2 ]

uses (a)(i) to state $E_{\mathrm{k}}=\frac{k e^{2}}{r} \mathcal{OR}$ states $E_{\mathrm{p}}=-\frac{2 k e^{2}}{r}$ adds $« E_{\mathrm{TOT}}=E_{\mathrm{k}}+E_{\mathrm{p}}=\frac{k e^{2}}{r}-\frac{2 k e^{2}}{r}$ » to get the result

(ii)

In this model the electron loses energy by emitting electromagnetic waves.

Describe the predicted effect of this emission on the orbital radius of the electron.

[ 2 ]

the total energy decreases OR by reference to $E_{\text {TOT }}=-\frac{k e^{2}}{r}$ the radius must also decrease

Marking guidance:

Award [0] for an answer concluding that radius increases

8.

b

i

with n=3, v= « $\sqrt{\frac{2 \times 8.99 \times 10^{9} \times\left(1.6 \times 10^{-19}\right)^{2}}{9.11 \times 10^{-31} \times 9 \times 2.7 \times 10^{-11}}}=$ » $1.44 \times 10^{6}$ « $\mathrm{ms}^{-1}$ »
$\lambda=\frac{6.63 \times 10^{-34}}{9.11 \times 10^{-31} \times 1.44 \times 10^{6}} \text { OR } \lambda=5.05 \times 10^{-10}<\mathrm{m} \gg$

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D.2.12 (HL)—Two-charge potential energy question 1

Question (a)

Question (i)

Question (ii)