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Physics Bootcamp

Section 50.7 Quantum Nature of Light Bootcamp

Exercises Exercises

Photon and Blackbody Radiation

9. Stefan-Boltzman law from Planck’s Radiation Law.
Follow the link: Checkpoint 50.7.
11. Electromagnetic Radiation Emitted by a Heated Tungsten Filament.
Follow the link: Checkpoint 50.15.
12. Temperature of the Universe from Cosmic Background Radiation.
Follow the link: Checkpoint 50.16.
14. Varying Intensity of Radiation with Temperature.
Follow the link: Checkpoint 50.18.
15. Varying Peak Wavelength of Radiation with Temperature.
Follow the link: Checkpoint 50.19.
17. Total Intensity of Cosmic Microwave Background.
Follow the link: Checkpoint 50.21.

Photoelectric effect

23. Stopping Potential and Photocurrent in Photoelectric Effect.
Follow the link: Checkpoint 50.31.
24. Finding the Value of Planck Constant from Photoelectric Effect.
Follow the link: Checkpoint 50.32.

Compton effect

27. Energy and Momentum of Scattered Electron in Compoton Experiment.
Follow the link: Checkpoint 50.38.
28. Wavelength of Scattered Photon from a Free-Electron Target.
Follow the link: Checkpoint 50.39.
29. Energy and Momentum of X-ray Scattered at Right Angle.
Follow the link: Checkpoint 50.40.
30. Energy and Momentum of Gamma RayScattered at Right Angle.
Follow the link: Checkpoint 50.41.

Miscellaneous

31. Temperature of an Oven from Blackbody Radiation Data TODO.
An oven is heated to a high temperature and the electromagnetic radiation coming out of the oven through a tiny hole in the oven is analyzed for radiance \(R_T(\lambda)\text{,}\) which is the power content per unit wavelength range per unit cross-section area of the hole. The data obtained at five wavelengths are:
\begin{align*} \amp (0.3\ \mu\textrm{m}, 1.1\times 10^{13}\:\textrm{W/m}^3),\\ \amp (0.4\ \mu\textrm{m}, 2.7\times 10^{13}\:\textrm{W/m}^3), \\ \amp (0.5\ \mu\textrm{m}, 3.8\times 10^{13}\:\textrm{W/m}^3), \\ \amp (0.6\ \mu\textrm{m}, 4.0\times 10^{13}\:\textrm{W/m}^3), \\ \amp (0.7\ \mu\textrm{m}, 3.7\times 10^{13}\:\textrm{W/m}^3), \\ \amp (0.8\ \mu\textrm{m}, 3.2\times 10^{13}\:\textrm{W/m}^3). \end{align*}
(a) Plot \(R_T\) versus \(\lambda\text{.}\) (b) From the data find the temperature of the oven. (c) Find the total power radiated per unit area of cross-section of the hole.
Hint.
Answer.
Solution.
32. Colision of a Photon with a Free Electron TODO.
A photon of energy \(hf\) collides head-on with a nearly free electron at rest. Let \(E_0\) be the rest energy of an electron. Show that the kinetic energy of the recoiled electron is given by
\begin{equation*} K = \dfrac{2h^2f^2}{2hf + E_0}. \end{equation*}
Hint.
Answer.
Solution.
33. Percentage of Energy that Photon can Transfer in Compton Scattering TODO.
(a) Prove that in the Compton scattering, a photon cannot transfer all of its energy to an electron. (b) Is there a maximum percentage of energy that a photon can transfer to an electron at rest? If so, what is it? If not, why not?
Hint.
Answer.
Solution.
34. Formula for Wavelength for Maximum Blackbody Radiation TODO.
(a) Treating \(R_T(\lambda)\) as a function of \(\lambda\text{,}\) prove that the maximum of the radiance occurs at a wavelength \(\lambda_{\textrm{max}}\) whose product with temperature is a constant.
\begin{equation*} \lambda_{\textrm{max}} = \textrm{constant}. \end{equation*}
(b) Find the value of the constant.
Hint.
Answer.
Solution.
35. Formula for Total Intensity of Blackbody Radiation TODO.
Integrate \(R_T(\lambda)\) over all values of \(0\le \lambda \le \infty\) to deduce the Stefan-Boltzmann law.
\begin{equation*} I = \int_0^\infty R_T(\lambda) d\lambda = \sigma T^4. \end{equation*}
Hint: Let \(x = hc/\lambda k_B T\text{.}\)
Hint.
Answer.
Solution.