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IB Physics: Quantum physics — Practice Questions & Answers
198 practice questions available for this topic — here are 10 with full answers and explanations.
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Practice questions with answers
1
Multiple choice · Medium
In the photoelectric effect, electrons are emitted only when the light frequency exceeds the:
- Threshold frequency
- Threshold wavelength minimum
- Maximum intensity
- Resonant frequency of the lattice
Tap an answer to check it.
WhyBelow the threshold frequency no electrons are emitted, regardless of intensity; above it, emission is immediate.
2
Multiple choice · Hard
The de Broglie wavelength of a particle of momentum $p$ is:
- $\lambda=\frac{h}{p}$
- $\lambda=\frac{p}{h}$
- $\lambda=hp$
- $\lambda=\frac{h}{p^{2}}$
Tap an answer to check it.
Why$\lambda=\frac{h}{p}$; matter exhibits wave-like behaviour with wavelength inversely proportional to momentum.
3
Multiple choice · Medium
In Einstein's photoelectric equation $E_{k,max}=hf-\Phi$, the term $\Phi$ is the:
- Work function
- Photon momentum
- Kinetic energy of the photon
- Planck constant
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Why$\Phi$ is the work function, the minimum energy needed to free an electron from the metal surface.
4
Fill in the blank · Medium
In the photoelectric equation $E_{k,max}=hf-\Phi$, the symbol $\Phi$ is called the work .
Answer:
function
WhyThe work function is the minimum energy required to liberate an electron from the metal.
5
Multiple choice · Hard
A tennis ball of mass 0.06 kg has kinetic energy 3 J. Which expression gives its de Broglie wavelength in metres?
- h divided by 0.6
- h divided by 3
- h divided by 0.06
- h divided by 0.36
Tap an answer to check it.
WhyMomentum p = sqrt(2 m KE) = sqrt(2 x 0.06 x 3) = sqrt(0.36) = 0.6, so lambda = h / 0.6.
6
Multiple choice · Medium
The de Broglie wavelength of a particle is inversely proportional to its
- momentum
- kinetic energy
- mass only
- speed only
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Whymomentum.
7
Fill in the blank · Medium
The de Broglie wavelength is given by lambda = h divided by .
Answer:
p / momentum
Whylambda = h / p (momentum).
8
Fill in the blank · Medium
Momentum can be found from kinetic energy using p = the square root of 2 m times .
Answer:
KE / kinetic energy
Whyp = sqrt(2 m KE).
9
Multiple choice · Hard
A photon of energy E strikes a metal of work function Phi and ejects an electron of mass m_e. What is the maximum possible speed of the photoelectron?
- square root of (2(E - Phi)/m_e)
- square root of (2E/m_e)
- square root of (E/m_e)
- square root of ((E - Phi)/m_e)
Tap an answer to check it.
WhyMaximum kinetic energy = E - Phi = half m_e v squared, so v = square root of (2(E - Phi)/m_e).
10
Multiple choice · Medium
In the photoelectric effect, the maximum kinetic energy of an emitted electron equals the photon energy minus the
- work function of the metal
- kinetic energy of the photon
- rest energy of the electron
- momentum of the photon
Tap an answer to check it.
WhyBy Einsteins equation, KE max = h f - work function.
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