Category Archives: Physics

You have a new summer job with NASA and are working on astronomical observations using electromagnetic radiation that is not in the visible range. Your supervisor has explained 21­cm radiation to you and that it is used for a number of observations of interstellar hydrogen. She explains that 21-cm radiation is in the microwave region of the electromagnetic spectrum and comes from a hyperfine splitting of the electron ground state of hydrogen. It is similar to the Zeeman effect, except that it is the spin states that are split, and the magnetic field is internal to the atom: it comes from the magnetic field due to the nucleus. When the atom makes a transition from the higher state to the lower state, a 21-cm photon is emitted. Based….

You are hired as an expert witness by the attorney representing a doctor. The doctor is being sued by a patient who claimed radiation damage from the doctor’s x-ray machine. The plaintiff argues that the machine must not have been properly shielded, exposing him to dangerous radiation. Your visit to the doctor’s office shows the following results. You do indeed measure x-radiation in the doctor’s office, with a minimum wavelength of 30.0 pm. Consultation with the doctor and inspection of his x-ray machine shows that it accelerates electrons through a voltage of 35.0 kV before they strike the target, producing bremsstrahlung. What advice do you give the attorney?

The Dulong–Petit law states that the molar specific heat of solids is 3R at higher temperatures, where R is the gas constant. For metals, this law is obeyed at room temperature, 300 K. The absorption of energy appears as internal energy in the metal in two primary ways: (1) vibration of metal lattice ions locked into crystalline positions and (2) translational kinetic energy of free electrons. The number of free electrons in a metal is approximately proportional to kBT/EF ,  since only those electrons near the Fermi energy can be thermally excited into available states. From this information, work with your group to determine the percentage of the total molar specific heat that is attributed to free electrons in gold.

Your group is a radiology department in a hospital. Two patients in your waiting room are arguing about who “got more radiation” in their cancer treatments. Patient A received 2.0 Gy of radiation, while Patient B received 1.0 Gy. Patient A is claiming that he had twice as much energy delivered to his body based on these numbers. Upon further investigation, it is determined that Patient A received radiation from fast neutrons, RBE 10, affecting 22 g of tissue. Patient B received alpha particles, RBE 18, affecting 30 g of tissue. (a) Who “got more radiation” in terms of biological effectiveness for radiation damage and (b) by what factor?

This activity simulates the statistical decay of radioactive nuclei. Packages of 100 dice can be purchased online. (a) First, think about the following procedure, but don’t do it yet: Put 100 dice in a bag and shake for a few seconds. Roll out the dice on a tabletop. Each such roll of the dice will represent one time interval Dt. Remove all the dice showing a one on the upper face, and set them aside. Record the remaining number N of dice. Put the remaining dice back in the bag, shake, and roll out again. Repeat this procedure, always removing the dice showing a number one from those on the table, until only a few dice remain. Second, after thinking about this procedure, predict the half-life of the….

You are working as a technician in the radiology department of a large hospital. One of the radioactive isotopes that is used to treat cancer is 60Co. Although use of this isotope is decreasing due to the availability of electrons from linear accelerators, 60Co is still in wide use where accelerators are not available. A radiologist has asked you to supply a container of 60Co, and you need to determine if a particular sample on the supply shelf is still viable for use. During your training, you learned that cobalt is not viable for medical use if its activity has fallen to 60.0% of its activity when delivered to the hospital. The label on the sample states that the delivery date was January 31, over three-and-a-half years ago. It is….

You are hired as an expert witness for the defense of an employee who is being sued for exposing his supervisor to harmful radiation. The employee had a PET scan and was injected at 4:30 PM with glucose containing on the order of 1014 atoms of 14O, with a half-life of 70.6 s. Immediately after the scan was completed, at 5:30 PM, the employee met his supervisor for a dinner meeting, shook hands with him, and sat down at the same table for dinner. The supervisor looked shocked when the employee mentioned that he had just had a PET scan before the meeting. Later that evening, the supervisor started feeling ill and became convinced that it was radiation poisoning due to the significant radiation he received during his encounter with….

You are performing work as an assistant to a cosmology professor. She asks you to estimate the temperature of the Universe at a time after the Big Bang when neutral atoms could form from the plasma and the Universe became transparent. She tells you that the energy required to excite an atom is on the order of 1 eV. She suggests you use the Boltzmann distribution function e-E/k BT to find the order of magnitude of the threshold temperature at which 1.00% of a population of photons has energy greater than 1.00 eV

A rocket engine for space travel using photon drive and matter–antimatter annihilation has been suggested. Suppose the fuel for a short-duration burn consists of N protons and N antiprotons, each with mass m. (a) Assume all the fuel is annihilated to produce photons. When the photons are ejected from the rocket, what momentum can be imparted to it? (b) What If? If half the protons and antiprotons annihilate each other and the energy released is used to eject the remaining particles, what momentum could be given to the rocket? (c) Which scheme results in the greater change in speed for the rocket?

You are working in an optical research laboratory. One of your projects involves the use of a double slit through which you pass orange laser light of wavelength 590 nm. Unfortunately, because of budget cuts, there are a lot of researchers in the same room, with lots of equipment stuffed in the room, and, in particular, lots of laser beams flying around the room. One day, you find that a second laser beam of unknown origin and different color is entering your double slit along with your orange beam and you are seeing an interference pattern that is the sum of those due to the two beams. You notice that the combined pattern is pretty much a mess, but wait! The m 5 3 maximum of your orange….