## AAMC physics question pack #114 and #119

jeffbassett87
Posts: 13
Joined: Mon Jan 13, 2020 7:38 pm

### AAMC physics question pack #114 and #119

#114-I don't understand the math of how they got the answer using the m=... equation. Especially where L=1/3.

#119-I didn't understand the AAMC reasoning at all.
NS_Tutor_Yuqi
Posts: 57
Joined: Fri May 29, 2020 11:43 pm

### Re: AAMC physics question pack #114 and #119

114: We know that we are trying to find the cavity mode number. Looking through the passage, the equation that would help us find that is mλm = 2L. We have L, the length of the laser cavity, which is 1/3m (this was given in the question). Although we don't have wavelength, the question gives us frequency and we can use the equation fm = c/λm, where c = 3 × 108 m/s, in order to find wavelength. From this, we get wavelength = 0.33 x 10-6m. Next, plug this back into the original formula in order to find m, which is the cavity mode number.

119: Be is undergoing electron capture here, where an electron is drawn into the nucleus and combines with a proton in order to create a neutron. Here, the mass number remains the same while the atomic number decreases by one. Therefore, the correct answer is Lithium with an atomic number of 3 and a mass number of 7.