Paper 1 Quantum Physics Answers

Q	Answer	Reason
1	A	Blackbody/photoelectric/line spectra etc. require quantum ideas.
2	D	Photon energy is $E=hf$.
3	B	Combining $E=hf$ with $f=c/\lambda$ gives $E=hc/\lambda$.
4	B	Photon energy is fixed by frequency.
5	C	Emission requires $hf\ge \Phi$, so $f\ge f_0$.
6	C	Energy conservation gives $hf=\Phi +K_{\max }$.
7	A	$e{V}_s=K_{max}$ for electrons.
8	B	Discrete photon energies imply discrete atomic levels.
9	D	Energy conservation gives $hf=\Delta E$.
10	A	Electron braking gives continuous X-rays.
11	A	Characteristic transitions are target-specific.
12	C	The largest photon energy comes from conversion of the full incident-electron kinetic energy.
13	B	Electron diffraction is evidence of wave behaviour.
14	D	The de Broglie relation is $\lambda =h/p$.
15	B	Fundamental quantum limit.
16	A	Localisation requires superposition of more momenta.
17	A	Absorption requires photon energy equal to an allowed energy-level difference.
18	A	The 9749 syllabus uses $\Delta p\Delta x\gtrsim h$.
19	A	A larger electron energy $eV$ permits a larger maximum photon energy, so ${\lambda }_{\min }=hc/(eV)$ decreases.
20	A	Target-specific energy-level transitions into inner-shell vacancies produce the characteristic lines.