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Atomic Spectra Uncertainties. A certain atom has an energy level \(2.58 \mathrm{cV}\) above the ground level. Once excited to this Ievel, the atom remains in this level for \(1.04 \times 10^{-7} \mathrm{~s}\) (on average) before emitting a photon and returning to the ground level. (a) What is the energy of the photon (in electron volts)? What is its wavelength (in nanomcters)? (b) What is the smallest possible uncertainty in energy of the photon? Give your answer in electron volts. (c) Show that \(|\Delta E| E|=| \Delta \lambda / \lambda \mid\) if \(|\Delta \lambda / \lambda|<1 .\) Use this to calculate the magnitude of the smallest possible uncertainty in the wavelength of the photon. Give your answer in nanometers.

Short Answer

Expert verified
Photon energy is 2.58 eV; wavelength is about 481 nm. Energy uncertainty is minimal, around \(4.8 \times 10^{-3}\) eV. Wavelength uncertainty is about \(0.9\) nm.

Step by step solution

01

Calculate Energy of the Photon

The energy of the photon emitted during the transition from the excited state to the ground state is equal to the difference in energy between these two states. Given the energy level of the excited state is 2.58 eV and assuming the ground state energy is 0 eV, the energy of the photon is 2.58 eV.
02

Calculate Wavelength Using Energy

Using the energy of the photon calculated in Step 1 and the relation \[ E = \frac{hc}{\lambda} \] where \( h \) is Planck's constant \( 4.135667696 \times 10^{-15} \text{ eV}\cdot\text{s} \) and \( c \) is the speed of light \( 3 \times 10^8 \text{ m/s} \), solve for the wavelength \( \lambda \):\[ \lambda = \frac{hc}{E} = \frac{4.135667696 \times 10^{-15} \times 3 \times 10^8}{2.58} \]Calculate \( \lambda \) and then convert the result to nanometers (1 m = 10鈦 nm).
03

Calculate Uncertainty in Energy

Use the uncertainty principle relation for energy, \[ \Delta E \cdot \Delta t \geq \frac{h}{4\pi} \] where \( \Delta t = 1.04 \times 10^{-7} \text{ s} \). Substituting the value of Planck's constant \( h = 6.62607015 \times 10^{-34} \text{ J}\cdot\text{s} \) converted to eV using 1 eV = 1.60218 脳 10鈦宦光伖 J, calculate \( \Delta E \).
04

Apply Ratio to Calculate Wavelength Uncertainty

From step 3, you have \( |\Delta E| \). Using the energy-wavelength relationship, we can relate this to the wavelength: \[ |\Delta E| / E = |\Delta \lambda / \lambda| \] Using the energy formulas, calculate \( |\Delta \lambda| \) as: \[ |\Delta \lambda| = \lambda \times \frac{\Delta E}{E} \] Substitute \( \lambda \) from Step 2 and \( \Delta E \) from Step 3 to find \(|\Delta \lambda|\) in nanometers.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Energy Levels
In atomic physics, energy levels refer to the discrete amounts of energy that an electron within an atom can possess. When an electron absorbs energy, it can jump from a lower energy level to a higher one, becoming "excited." Conversely, it releases energy as a photon when it falls back to a lower energy level or the ground state.
In the case of our exercise, the atom has been excited to an energy level that is 2.58 electron volts (eV) above the ground state. This energy is an intrinsic property of the atom's electron configuration and determines the energy of the photon emitted when the electron returns to the ground state.
Understanding energy levels is crucial because they help predict the behavior of atoms in different conditions, such as light absorption and emission.
Photon Emission
Photon emission occurs when an excited electron returns to a lower energy state, typically the ground state, by releasing the excess energy as a photon. This process is observable in spectra as discrete lines, each representing a specific transition.
In the related exercise, after average time of \(1.04 \times 10^{-7}\) seconds at the excited state, the atom emits a photon with an energy of 2.58 eV. The energy of the photon corresponds precisely to the difference in energy between the excited and ground state levels.
Photon emission is fundamental to understanding phenomena like fluorescence and the colors produced by different elements when burned. It also forms the basis for technologies such as lasers and LED lights.
Uncertainty Principle
The Uncertainty Principle, introduced by Werner Heisenberg, is a fundamental concept of quantum mechanics. It states that certain pairs of properties, such as energy and time, cannot both be measured precisely at the same time. This principle applies to the energies and lifetimes of excited states in atoms.
In our textbook problem, we calculate the smallest possible uncertainty in the energy of the photon using the formula: \[ \Delta E \cdot \Delta t \geq \frac{h}{4\pi} \] where \( \Delta t \) is the time the atom spends in the excited state and \( h \) is Planck's constant. This relation allows us to estimate the energy's uncertainty, considering the brief duration (\(1.04 \times 10^{-7}\) seconds) that the atom remains excited.
This principle reflects the inherent limitations in predicting quantum-scale events and illustrates nature's probabilistic behavior at the microscopic level.
Wavelength Calculation
To find the wavelength of the photon emitted, we use the relationship between energy and wavelength given by the equation:\[ E = \frac{hc}{\lambda} \] where \( E \) is the energy of the photon, \( h \) is Planck's constant, and \( c \) is the speed of light. Solving this equation for wavelength \( \lambda \) provides:\[ \lambda = \frac{hc}{E} \]By substituting in the values, including the photon energy of 2.58 eV, we calculate the wavelength in nanometers.
Additionally, we determine the uncertainty in wavelength \( \Delta \lambda \) using the relation:\[ |\Delta E| / E = |\Delta \lambda / \lambda| \] This correlation allows us to relate energy uncertainty to wavelength uncertainty, enabling us to calculate \( |\Delta \lambda| \) based on the previously determined \( \Delta E \).
Understanding this calculation is essential in fields such as spectroscopy, where precise wavelength measurement is necessary for identifying and analyzing materials. It connects the quantum concept of energy levels with the classical scope of wave phenomena.

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Most popular questions from this chapter

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(a) A particle with mass \(m\) has kinetic energy equal to three times its rest encrgy. What is the de Broglic wavelength of this particle? (Hint: You must use the relativistic expressions for momentum and kinetic energy: \(E^{2}=(p c)^{2}+\left(m c^{2}\right)^{2}\) and \(K=E-\) \(m c^{2} \cdot(b)\) Determine the numerical value of the kinetic energy (in Mev) and the wavelength (in meters) if the particle in part (a) is (i) an electron and (i) a proton.

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