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X rays are produced in a tube operating at 24.0 kV. After emerging from the tube, x rays with the minimum wavelength produced strike a target and undergo Compton scattering through an angle of 45.0\(^\circ\). (a) What is the original x-ray wavelength? (b) What is the wavelength of the scattered x rays? (c) What is the energy of the scattered x rays (in electron volts)?

Short Answer

Expert verified
(a) \(3.24 \times 10^{-11}\, m\); (b) \(3.31 \times 10^{-11}\, m\); (c) 3750 eV.

Step by step solution

01

Calculate the original X-ray wavelength

The energy of the X-rays in the tube is given by the voltage, 24.0 kV. First, convert this voltage to energy using the formula: \( E = eV \), where \( e = 1.60 \times 10^{-19} \) C (electron charge) and \( V = 24000 \) V. Calculate \( E = 1.60 \times 10^{-19} \times 24000 = 3.84 \times 10^{-15} \) J. Then, use the energy-wavelength relationship for photons: \( E = \frac{hc}{\lambda} \), where \( h = 6.626 \times 10^{-34} \) Js (Planck's constant) and \( c = 3.00 \times 10^8 \) m/s. Solve for \( \lambda \):\[ \lambda = \frac{hc}{E} = \frac{6.626 \times 10^{-34} \times 3.00 \times 10^8}{3.84 \times 10^{-15}} \approx 3.24 \times 10^{-11} \text{ m}\] This is the original X-ray wavelength.
02

Calculate the wavelength of the scattered X-rays

Use the Compton scattering formula: \[ \lambda' - \lambda = \frac{h}{mc} (1 - \cos \theta) \] where \( \lambda' \) is the wavelength after scattering, \( m \) is the electron mass \(9.11 \times 10^{-31}\) kg, and \( \theta = 45^\circ \). Substitute known values: \[ \lambda' - 3.24 \times 10^{-11} = \frac{6.626 \times 10^{-34}}{9.11 \times 10^{-31} \times 3.00 \times 10^8} (1 - \cos 45^\circ) \]\[ \lambda' - 3.24 \times 10^{-11} = 2.43 \times 10^{-12} \times 0.292 \]\[ \lambda' - 3.24 \times 10^{-11} \approx 7.1 \times 10^{-13} \]\[ \lambda' \approx 3.31 \times 10^{-11} \text{ m} \] This is the wavelength of the scattered X-rays.
03

Calculate the energy of the scattered X-rays

Use the energy-wavelength formula again: \[ E' = \frac{hc}{\lambda'} = \frac{6.626 \times 10^{-34} \times 3.00 \times 10^8}{3.31 \times 10^{-11}} \] Calculate: \[ E' \approx 6.00 \times 10^{-16} \text{ J} \] Convert to electron volts (1 eV = \(1.60 \times 10^{-19}\) J): \[ E' \approx \frac{6.00 \times 10^{-16}}{1.60 \times 10^{-19}} \approx 3750 \text{ eV} \] This is the energy of the scattered X-rays in electron volts.

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Key Concepts

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

X-ray production
X-ray production is a fascinating process that typically occurs in a vacuum tube when high-energy electrons collide with a metal target. These electrons are accelerated by a high voltage, in this case, 24 kV, which gives them sufficient energy to knock away inner-shell electrons from the target atoms.

When these electrons from the target material fill the vacated lower energy levels, X-rays are emitted. These are high-frequency electromagnetic waves with very short wavelengths, capable of penetrating various substances.

The X-rays produced directly in this manner are dependent on the voltage applied within the tube, indicating that higher voltages lead to higher energy X-rays. This relationship is crucial for calculating the original X-ray wavelength, as seen in our exercise.
Wavelength calculation
To determine the wavelength of X-rays, we start by using the energy-wavelength relationship: the energy of X-rays is calculated from the voltage in electron volts converted to joules. We then apply the formula for photon energy \[ E = \frac{hc}{\lambda} \] where \( h \) is Planck's constant and \( c \) is the speed of light.

By inserting the known values and solving for \( \lambda \), we find the minimum wavelength of the X-rays produced in the tube. Here, the solution came out to be approximately \( 3.24 \times 10^{-11} \text{ m} \). Understanding this calculation is essential as it links the X-ray's energy to its frequency and wavelength, showing how high energy corresponds to short wavelengths.
Energy conversion
Converting energy into different units helps make complex problem-solving clearer and universally understandable. In Compton scattering problems, we often deal with energy in different forms, primarily in joules and electron volts.

The electron volt (eV) is a convenient unit used for very small energy scales and is defined as the energy gained by an electron when it is accelerated through a potential difference of 1 volt. For example, in the step-by-step solution, the energy of the scattered X-rays was initially found in joules and converted to electron volts to determine it as approximately 3750 eV.

This conversion is pivotal for physics applications, especially in the context of X-ray spectroscopy, where energy measurements are directly linked to wavelengths.
Photon energy
Photon energy is a cornerstone concept in the study of electromagnetic waves like X-rays. It is defined by the relationship \[ E = \frac{hc}{\lambda} \] where \( E \) is energy, \( h \) is Planck's constant, and \( \lambda \) is the wavelength.

This relationship displays that energy is inversely proportional to wavelength: as the energy of a photon increases, its wavelength decreases. For example, in our original unscattered X-rays, the short wavelength derived suggests high energy. After scattering, the wavelength increased slightly, indicating a corresponding reduction in energy.

Understanding this formula is key to mastering the changes in energy states during Compton scattering.
Scattering angle
The scattering angle in Compton scattering scenarios is significant because it dictates how much the wavelength of the X-ray changes post-scattering. In our exercise, the X-ray was scattered at an angle of 45 degrees.

The Compton wavelength shift formula, given by \[ \Delta \lambda = \frac{h}{mc} (1 - \cos \theta) \] quantifies how this angle influences the change in wavelength (\( \Delta \lambda \)). Here, \( m \) is the electron mass and \( \theta \) the scattering angle. Solving with a 45-degree angle produces a change in wavelength that affects the energy of the scattered photon.

Smaller angles result in smaller wavelength changes, whereas larger angles result in more significant shifts, illustrating the nuanced nature of X-ray behavior during interactions with matter.

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Most popular questions from this chapter

Nuclear fusion reactions at the center of the sun produce gamma-ray photons with energies of about 1 MeV (10\(^6\) eV). By contrast, what we see emanating from the sun's surface are visiblelight photons with wavelengths of about 500 nm. A simple model that explains this difference in wavelength is that a photon undergoes Compton scattering many times-in fact, about 10\(^{26}\) times, as suggested by models of the solar interior-as it travels from the center of the sun to its surface. (a) Estimate the increase in wavelength of a photon in an average Compton-scattering event. (b) Find the angle in degrees through which the photon is scattered in the scattering event described in part (a). (\(Hint\): A useful approximation is cos \(\phi \approx 1 - \phi^2 /2\), which is valid for \(\phi \ll\) 1. Note that \(\phi\) is in radians in this expression.) (c) It is estimated that a photon takes about 10\(^6\) years to travel from the core to the surface of the sun. Find the average distance that light can travel within the interior of the sun without being scattered. (This distance is roughly equivalent to how far you could see if you were inside the sun and could survive the extreme temperatures there. As your answer shows, the interior of the sun is \(very\) opaque.)

The cathode-ray tubes that generated the picture in early color televisions were sources of x rays. If the acceleration voltage in a television tube is 15.0 kV, what are the shortest-wavelength x rays produced by the television?

X rays with initial wavelength 0.0665 nm undergo Compton scattering. What is the longest wavelength found in the scattered x rays? At which scattering angle is this wavelength observed

An incident x-ray photon of wavelength 0.0900 nm is scattered in the backward direction from a free electron that is initially at rest. (a) What is the magnitude of the momentum of the scattered photon? (b) What is the kinetic energy of the electron after the photon is scattered?

A horizontal beam of laser light of wavelength 585 nm passes through a narrow slit that has width 0.0620 mm. The intensity of the light is measured on a vertical screen that is 2.00 m from the slit. (a) What is the minimum uncertainty in the vertical component of the momentum of each photon in the beam after the photon has passed through the slit? (b) Use the result of part (a) to estimate the width of the central diffraction maximum that is observed on the screen.

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