Modern Physics unit test
A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.
Why fusion and fission both release energy
Binding energy conversion
Counting halvings
Binding energy PER NUCLEON is the meaningful figure
The 1240 eV·nm shortcut
Photoelectric threshold
de Broglie wavelength
Energy level diagrams
Intensity versus frequency
Why the electronvolt exists
Alpha versus beta decay
Energy level transitions
Short answer 1. Define or explain: Fission vs fusion
3 ptsShort answer 2. Define or explain: Work function
3 ptsShort answer 3. Define or explain: Absorption versus emission spectra
3 ptsShort answer 4. Define or explain: Why the photon model was needed
3 ptsFree response
12 ptsIn a photoelectric effect experiment, light of various frequencies is shone on a metal surface and the maximum kinetic energy of the emitted electrons is measured. The data produce a straight line when maximum kinetic energy is plotted against frequency: the line crosses the frequency axis at f₀ = 5.5 × 10¹⁴ Hz and has a positive slope.
A. Describe the graph of maximum kinetic energy versus frequency, including its shape, its intercepts, and the physical meaning of its slope.
B. Derive an expression for the work function of the metal in terms of the threshold frequency f₀ and physical constants, and calculate its value in electron volts.
C. Describe how the graph would change if the intensity of the incident light were doubled while its frequency was held constant, and explain why.
D. Describe how the graph would change if a different metal with a larger work function were used, and explain why.