# Quantum Physics

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Questions: 10 | Attempts: 1,871

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IB Physics

• 1.

B.
• 2.

### When electrons of suitable energy travel through a thin layer of graphite, a pattern of concentric circles is produced on a screen. The production of this pattern is evidence for

• A.

The wave nature of the electron

• B.

The nuclear model of the atom.

• C.

The particle nature of the electron.

• D.

The existence of X-rays

A. The wave nature of the electron
Explanation
When electrons of suitable energy travel through a thin layer of graphite, a pattern of concentric circles is produced on a screen. This phenomenon is known as electron diffraction and is consistent with the wave nature of electrons. The pattern of concentric circles is similar to the interference patterns produced by waves, indicating that electrons exhibit wave-like behavior. This supports the idea that electrons can behave both as particles and waves, and provides evidence for the wave nature of the electron.

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• 3.

### The graph shows the variation with frequency f of the maximum kinetic energy Ek of photoelectrons emitted from a metal surface S. Which one of the following graphs shows the corresponding variation for a metal surface with a higher work function? The dotted line on each graph shows the variation for metal S.

B.
Explanation
The correct answer would be graph B. This is because a higher work function means that more energy is required to remove an electron from the metal surface. Therefore, the maximum kinetic energy of the photoelectrons would be higher for a metal with a higher work function. This is represented by the higher values of Ek on graph B compared to graph A.

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• 4.

### An α-particle having a de Broglie wavelength λi collides with a stationary carbon nucleus. The α-particle moves off in a different direction as shown below. After the collision, the de Broglie wavelengths of the α-particle and the carbon nucleus are λf and λc respectively. Which of the following is a true statement related to the de Broglie wavelengths?

• A.

Î»i < Î»f

• B.

Î»i > Î»f

• C.

Î»f = Î»c

• D.

Î»i = Î»c

A. Î»i < Î»f
Explanation
The de Broglie wavelength is inversely proportional to the momentum of a particle. Since the alpha particle is initially moving and the carbon nucleus is stationary, the alpha particle has momentum while the carbon nucleus has zero momentum. After the collision, the alpha particle moves off in a different direction, indicating a change in momentum. As momentum increases, the de Broglie wavelength decreases. Therefore, the de Broglie wavelength of the alpha particle after the collision (λf) is smaller than the de Broglie wavelength before the collision (λi).

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• 5.

### Which one of the following best shows the variation with kinetic energy E of the de Broglie wavelength λ associated with a particle?

B.
Explanation
The de Broglie wavelength of a particle is inversely proportional to its kinetic energy. This means that as the kinetic energy of a particle increases, its de Broglie wavelength decreases. Conversely, as the kinetic energy decreases, the de Broglie wavelength increases. Therefore, the correct answer would be the option that shows a decreasing trend between kinetic energy and de Broglie wavelength.

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• 6.

### An electron is accelerated from rest through a potential difference V. Which one of the following best shows the variation of the de Broglie wavelength l of the electron with potential difference V?

D.
Explanation
The de Broglie wavelength of an electron is inversely proportional to its momentum. As the electron is accelerated through a potential difference V, its kinetic energy and momentum increase. Therefore, the de Broglie wavelength of the electron decreases as the potential difference V increases. This is represented by option B, where the wavelength decreases as V increases.

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• 7.

### The diagram below shows some possible electron transitions between three principal energy levels in the hydrogen atom. Which electron transition is associated with the absorption of a photon of the longest wavelength?

• A.

A

• B.

B

• C.

C

• D.

D

B. B
Explanation
The electron transition associated with the absorption of a photon of the longest wavelength is represented by option B in the diagram. This is because the longer the wavelength of a photon, the lower its energy. In option B, the electron is transitioning from the third energy level to the second energy level, which requires the absorption of a photon with lower energy. Therefore, this transition corresponds to the absorption of a photon with the longest wavelength.

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• 8.

### The diagram below shows three energy levels of a certain atom.

• A.

1/3

• B.

1/2

• C.

2

• D.

3

C. 2
Explanation
The energy levels of an atom are represented by the numbers 1/3, 1/2, 2, and 3. The correct answer is 2, which indicates that the atom is in the second energy level. This means that the atom has absorbed or released an amount of energy that corresponds to the transition between the first and second energy levels.

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• 9.

### The diagram below shows four energy levels in an atom, together with some possible electron transitions. Which one of the following best represents the emission line spectrum produced from these transitions?

A.
Explanation
The diagram shows four energy levels in an atom and the possible electron transitions between them. The emission line spectrum represents the specific wavelengths of light emitted when an electron moves from a higher energy level to a lower energy level. The correct answer would be the diagram that shows discrete lines at specific wavelengths, indicating that only certain transitions are occurring. This is because each transition corresponds to a specific energy difference between the energy levels, resulting in the emission of light at a specific wavelength.

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• 10.

### Light is incident on two different metal surfaces L and H. The metals are in a vacuum. The surface L has a lower work function energy than surface H.          Which of the following graphs best shows the variation with frequency f of the maximum kinetic energy EMAX of photo-electrons emitted from both surfaces.

C.
Explanation
The graph that best shows the variation with frequency f of the maximum kinetic energy EMAX of photo-electrons emitted from both surfaces would be a straight line with a positive slope. This is because the maximum kinetic energy of photo-electrons is directly proportional to the frequency of the incident light. As the frequency increases, the maximum kinetic energy of the photo-electrons also increases. Since surface L has a lower work function energy than surface H, it would require less energy for electrons to be emitted from surface L compared to surface H. Therefore, the graph for surface L would start at a lower maximum kinetic energy compared to surface H.

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