NESA Physics Light: Quantum Model
15 sample questions with marking guides and sample answers · Avg. score: 66.4%
Many scientists have performed experiments to explore the interaction of light and matter.
Analyse how evidence from at least THREE such experiments has contributed to our understanding of physics.
Reveal Answer
Answers could include:
Reference to:
- Black body radiation experiments and the development of quantum physics
- Photoelectric experiments and the development of quantum physics
- Spectroscopy experiments and the development of astrophysics and the atomic model
- Polarisation experiments and the development of the wave nature of light
- Interference and diffraction and the development of the wave model of light
- Cosmic gamma rays and the development of theory of special relativity and/or the standard model.
| Descriptor | Marks |
|---|---|
| 8 |
| 7 |
The student response meets all criteria of the 5-mark band, and additionally meets the majority of criteria in the 7-mark band. | 6 |
| 5 |
The student response meets all criteria of the 3-mark band, and additionally meets the majority of criteria in the 5-mark band. | 4 |
Provides some information about evidence from an experiment AND/OR a link to physics | 3 |
The student response meets all criteria of the 1-mark band, and additionally meets the majority of criteria in the 3-mark band. | 2 |
Provides some relevant information | 1 |
None of the above | 0 |
Describe what happens when light is shone onto a metallic surface in the context of the photoelectric effect.
Reveal Answer
Light with energy equivalent to has the ability to produce photoelectrons from a metallic surface.
When the frequency of light is below the threshold frequency for the metallic surface, the light will be reflected with no transfer of energy.
When the frequency of light is above the threshold frequency for the metallic surface, the energy of the photons will be absorbed and photoelectrons with kinetic energy proportional to the excess energy will be released.
The intensity of incident light is proportional to the number of photoelectrons for frequencies greater than the threshold frequency.
| Descriptor | Marks |
|---|---|
Identifies incident light has energy equivalent to | 1 |
Describes transfer of energy when frequency of light is below the threshold frequency | 1 |
Describes transfer of energy when frequency of light is above the threshold frequency | 1 |
Identifies relationship between intensity of incident light and resultant photoelectrons | 1 |
Determine the wavelength of an electromagnetic wave with an energy of J.
m
m
m
m
Reveal Answer
m
This incorrect value results from simply multiplying the energy by the speed of light (), ignoring Planck's constant and the correct formula.
m
This answer is obtained by dividing Planck's constant by the energy () but neglecting to multiply by the speed of light ().
m
Using the relationship , substitute Planck's constant ( Js) and the speed of light ( m/s) to find m.
m
This value represents the wavenumber ( m), which is the reciprocal of the wavelength rather than the wavelength itself.
A black body at a temperature of 6040 K produces photons across a range of frequencies.
Calculate the frequency at which the maximum number of photons is produced.
Hz
Hz
Hz
Hz
Reveal Answer
Hz
This is the correct frequency corresponding to the peak wavelength. Using Wien's Displacement Law, , and converting to frequency using yields .
Hz
This value results from incorrectly dividing the temperature by Wien's constant () without involving the speed of light, which does not yield a frequency.
Hz
This value represents the peak wavelength in meters (), not the frequency. You likely forgot to convert wavelength to frequency using .
Hz
This value is the period of the wave (), which represents the time for one cycle, rather than the frequency.
Discuss the nature of light by describing evidence from two key experiments.
Reveal Answer
Young's double slit experiment and black-body radiation both provide evidence for the behaviour of light.
In Young's double slit experiment, the interference patterns formed as light passed between the two slits demonstrates the wave nature of light.
In contrast, black-body radiation demonstrates the quantised nature of light as electrons can only absorb or emit energy in discrete amounts.
Therefore, light has some wave properties and some particle properties.
| Descriptor | Marks |
|---|---|
Identifies evidence for the nature of light comes from Young's double slit experiment | 1 |
Identifies evidence for the nature of light comes from black-body radiation | 1 |
Describes evidence for wave nature of light | 1 |
Describes evidence for photons | 1 |
Concludes light has the properties of both waves and particles | 1 |
The maximum kinetic energy of an electron ejected from a metallic surface can be increased by
using a positively ionised metal.
using a metal with a larger work function.
increasing the intensity of the incident light.
decreasing the wavelength of the incident light.
Reveal Answer
using a positively ionised metal.
Using a positively ionised metal would increase the electrostatic attraction on the electrons, effectively increasing the energy required to escape and decreasing the kinetic energy.
using a metal with a larger work function.
According to the photoelectric equation , increasing the work function () reduces the remaining energy available for kinetic energy.
increasing the intensity of the incident light.
Increasing intensity increases the number of photons and ejected electrons (photocurrent), but does not change the energy of individual photons or the maximum kinetic energy of the electrons.
decreasing the wavelength of the incident light.
Photon energy is inversely proportional to wavelength (). Decreasing the wavelength increases the incident photon energy, thereby increasing the maximum kinetic energy of the ejected electrons.
A hot iron bar was observed to have a deep red colour. As the iron bar was heated further, the colour changed to orange.
Explain the observed colour change in terms of black-body radiation.
Reveal Answer
The iron bar represents a model of black-body radiation, where the spectrum of radiation emitted is due to the conversion of the object’s thermal energy. This is outlined by Wien’s Law, where .
As the temperature increases, the peak wavelength will be shorter and this is observed by the colour change from red to orange.
| Descriptor | Marks |
|---|---|
Describes the scenario in terms of black-body radiation | 1 |
Uses Wien’s Law to explain the colour change in the iron bar | 1 |
Which one of the following best provides evidence of light behaving as a particle?
photoelectric effect
white light passing through a prism
diffraction of light through a single slit
interference of light passing through a double slit
Reveal Answer
photoelectric effect
The photoelectric effect demonstrates that light energy is absorbed and emitted in discrete quantized packets called photons, providing direct evidence of its particle nature.
white light passing through a prism
White light passing through a prism demonstrates dispersion and refraction, which are phenomena explained by the wave nature of light and its varying wavelengths.
diffraction of light through a single slit
Diffraction is the bending of light as it passes through a slit, which is a classic characteristic of waves rather than particles.
interference of light passing through a double slit
Interference patterns are created by the superposition of overlapping waves, providing foundational evidence for the wave model of light.
Incident light with a frequency of Hz is shone onto a metal surface with a work function of J.
Determine the kinetic energy of a photoelectron ejected from the metal surface.
eV
eV
eV
eV
Reveal Answer
eV
This is the correct answer. First, calculate the photon energy J. Subtract the work function to find the kinetic energy in Joules ( J), then divide by J/eV to convert to electron-volts.
eV
This option is incorrect. It appears to confuse the numerical value of the frequency () with the final energy, ignoring Planck's constant and the necessary unit conversions.
eV
This option represents the kinetic energy in Joules ( J), not electron-volts. To obtain the correct answer in eV, you must divide this value by the elementary charge ( J/eV).
eV
This value is extremely small and physically unrealistic for the kinetic energy of a photoelectron in this context. It likely results from an arithmetic error or incorrect formula application.
Identify the defining feature of a black body.
All frequencies of electromagnetic radiation are absorbed and emitted.
Light with two wavelength peaks is emitted at a specific temperature.
Electrons are emitted in the presence of all frequencies of light.
The peak of its spectral output does not vary with temperature.
Reveal Answer
All frequencies of electromagnetic radiation are absorbed and emitted.
A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence, and emits radiation across a continuous spectrum based on its temperature.
Light with two wavelength peaks is emitted at a specific temperature.
The spectral distribution of black-body radiation is a continuous curve with a single peak intensity wavelength determined by the temperature, not two peaks.
Electrons are emitted in the presence of all frequencies of light.
This describes a misunderstood version of the photoelectric effect; a black body is defined by its perfect absorption and thermal emission of electromagnetic radiation, not by electron emission.
The peak of its spectral output does not vary with temperature.
According to Wien's Displacement Law, the peak wavelength of emission is inversely proportional to temperature (), meaning the peak shifts to shorter wavelengths as the object gets hotter.
Two experiments were conducted, and the following observations were made.
| Experiment 1 | Light passing through a double slit produces a diffraction pattern. |
| Experiment 2 | Above a specific frequency, light incident on a metallic surface produces photoelectrons with discrete amounts of energy. |
Which statement can be supported by the observations?
A wave theory of light can completely describe the nature of light.
The bending of light is a result of light behaving as a particle.
The particle model only describes some properties of light.
Only light waves can travel in a vacuum.
Reveal Answer
A wave theory of light can completely describe the nature of light.
This is incorrect because Experiment 2 (the photoelectric effect) demonstrates particle-like behavior that cannot be explained by the wave theory of light.
The bending of light is a result of light behaving as a particle.
This is incorrect because the bending of light (diffraction) observed in Experiment 1 is a characteristic behavior of waves, not particles.
The particle model only describes some properties of light.
This is correct because the particle model explains the photoelectric effect in Experiment 2 but cannot explain the diffraction pattern in Experiment 1, showing it is an incomplete description.
Only light waves can travel in a vacuum.
This is incorrect because the observations provided do not address travel in a vacuum, and light travels through a vacuum regardless of the model used to describe it.
The photoelectric effect is mathematically modelled by the following relationship:
In this model, the symbol represents the amount of energy
supplied by a photon to an electron.
retained by an electron after being hit.
required to release an electron from a material.
left over after a collision of a photon with an electron.
Reveal Answer
supplied by a photon to an electron.
Incorrect. The energy supplied by the incident photon is represented by the term , not .
retained by an electron after being hit.
Incorrect. The energy retained by the electron as kinetic energy after being ejected is represented by .
required to release an electron from a material.
Correct. The symbol represents the work function, which is the minimum energy required to overcome the attractive forces and release an electron from the material.
left over after a collision of a photon with an electron.
Incorrect. The energy left over after freeing the electron becomes its maximum kinetic energy, represented by .
Describe how experiments on the photoelectric effect provide evidence of the quantised nature of photons.
Reveal Answer
The photoelectric effect experiment demonstrates that the number of electrons ejected from a metal plate is proportional to the intensity of incident light, whereas the kinetic energy of the ejected electrons is proportional to the frequency of incident light. The fact that frequencies lower than a threshold value will not eject an electron suggests that light energy is quantised. As the frequency increases, the kinetic energy of the ejected electrons increases, suggesting that light can be conceived as packets of energy (photons). The fact that a greater intensity of light causes more electrons to be ejected suggests that the greater the intensity, the more photons (or packets of energy) are incident on the metal plate, also confirming the idea of light as a photon.
Description of Features
Marking Bands| Descriptor | Marks |
|---|---|
Describes three relevant features of the photoelectric effect. | 3 |
Describes two relevant features of the photoelectric effect. | 2 |
Describes one relevant feature of the photoelectric effect. | 1 |
None of the above | 0 |
Evidence of Quantisation
Marking Bands| Descriptor | Marks |
|---|---|
Identifies how two relevant features provide evidence of quantisation of photons. | 2 |
Identifies how one relevant feature provides evidence of quantisation of photons. | 1 |
None of the above | 0 |
Calculate the frequency of light that would be required to eject a photoelectron at a velocity of m s from a metal plate with a work function of 4.73 eV.
Hz
Hz
Hz
Hz
Reveal Answer
Hz
This value represents the threshold frequency calculated using only the work function (), ignoring the additional energy required for the electron's kinetic velocity.
Hz
This incorrect answer results from subtracting the work function energy from the kinetic energy (or vice versa) instead of adding them to determine the total photon energy.
Hz
This calculation incorrectly equates the photon energy solely to the electron's kinetic energy (), neglecting the work function energy required to eject the electron from the metal.
Hz
According to the photoelectric equation , the photon energy is the sum of the work function (converted to Joules) and the kinetic energy. Solving for frequency yields Hz.
What evidence resulting from investigations into the photoelectric effect is consistent with the model of light subsequently proposed by Einstein?
Photoelectrons were only ejected from a metal if the light was less than a specific wavelength.
Increasing the intensity of light on a metal increased the maximum kinetic energy of the photoelectrons.
If photons had sufficient energy to eject photoelectrons from a metal, the maximum kinetic energy was independent of the type of metal used.
The probability of photoelectrons being emitted from a metal was proportional to the duration of exposure to light for any given wavelength used.
Reveal Answer
Photoelectrons were only ejected from a metal if the light was less than a specific wavelength.
Einstein's model states that light consists of photons with energy inversely proportional to wavelength (). Electrons are only ejected if a single photon has enough energy to overcome the metal's work function, which requires the light to have a wavelength shorter than a specific threshold.
Increasing the intensity of light on a metal increased the maximum kinetic energy of the photoelectrons.
In the photon model, increasing light intensity increases the number of photons (and thus the number of ejected electrons), but it does not change the energy of individual photons or the maximum kinetic energy of the electrons.
If photons had sufficient energy to eject photoelectrons from a metal, the maximum kinetic energy was independent of the type of metal used.
The maximum kinetic energy of ejected electrons depends on the metal's work function (), which is a property that varies depending on the specific type of metal used.
The probability of photoelectrons being emitted from a metal was proportional to the duration of exposure to light for any given wavelength used.
According to the photon model, if the light's wavelength is above the threshold, no electrons will be emitted regardless of how long the metal is exposed to the light, because individual photons lack the energy to eject an electron.