A standard electrical plug fits into an outlet in only one way because one of the two prongs is larger than the other. This ensures that people will insert the plug properly to create a grounded circuit. This is an example of:

The atoms in a nickel crystal vibrate as harmonic oscillators with an angular frequency of 2.3 × 1013 rad/s. the mass of a nickel atom is 9.75 × 10-26 kg. what is the difference in energy between adjacent vibrational energy levels of nickel? (h = 6.626 × 10-34 j • s, , 1 ev = 1.60 × 10-19 j)