Two-Minute Problems

Remember to give a good explanation, no longer than two sentences.

1. Q3T.2: Review the discussion of the wave model predictions in Sec. Q3.3.
2. Q3S.2: How is the intensity of the light related to the number of photons per second? Be careful, the energy per photon depends on the frequency!

Chapter Q Problems

• Q3B.5: What can you say about the electron kinetic energy when they are just ejected? How does W come in?
• Q3S.3: How do you convert a number for power=energy/second into one for number per second?
• Q3S.4: Similar to the problem done in class. How is the maximum voltage developed related to the maximum kinetic energy of electrons liberated? What equation relates maximum kinetic energy to the wavelength of the incident light? If you have two data points, is that enough to find hc and W?
• Q3R.1: How many photons per second must the eye register from the star in order to "see" it? How many photons per second does the star emit? How does the distance of the star come into the game? You'll need to estimate an average energy for the photons from the sun; you can do this by assuming an "average" wavelength.
• Q3A.1: 4-momentum is a 4-component vector (E/c**2,px,py,pz) which energy and 3-momentum in the same way as the position 4-vector (ct,x,y,z) combines time and space. In SR units, c=1, and the momentum 4-vector reads (E,px,py,pz). So in Eq. (Q3.20), the first line describes energy conservation, the second line px conservation, and so on. Figure out which of the four terms in Eq. (Q3.20) describes the 4-momentum of the electron (photon) before and after the collision. For part (d), you must return to SI units by setting E -> E/c**2 in the 4-momentum.