The document contains 3 physics problems. Problem 1 asks about the sound level experienced from 5 people each 1 meter away all talking at 60 dB. The answer is 81 dB. Problem 2 asks about the potential energy and electric potential of an electron moving in an electric field. The answer is C - potential energy increases and electric potential increases. Problem 3 asks which Gaussian surfaces have zero electric flux. The answer is surfaces A and D, as the net charge enclosed within each of these surfaces is zero.

1. Problem 1 (7 points) The sound level at 1.0 m from a certain talking person talking is 60 dB.
You are surrounded by fixe such people, all 1.0 m from you and all talking equally loud at the
same time. What sound level are you being exposed to? You can neglect any absorption,
reflection, or interference of the sound. The threshold of hearing is 1.0 102 w A) 74 dB B) 300
dE C)81 dB D) 60 dB E) 67 dB Problem 2: (6 points) For an electron moving in the direction of
the electric field A) its potential energy increases and its electric potential decreases. B) its
potential energy decreases and its electric potential decreases. C) its potential energy increases
and its electric potential increases. D) its potential energy decreases and its electric potential
increases. E) its potential energy and its electric potential remain the same. Problem 3: (6 points)
The figure shows four Gaussian surfaces (A, B, C, and D), surrounding a distribution of charges.
Which Gaussian surfaces have zero electric flux through them? A) Only surface A +3g B) Only
Surface D 24 C) Surfaces A and B D) Surfaces B and D. E) Surfaces A and D
Solution
3) according to gauss law ,
electric flux is epsilon naught times the charge enclosed by the surface
so Electric flux will be zero for a surface where charge enclosed in zero
for surface A - +3q - 2q + 2q - q - 2q = 0
for surface D = -2q + 2q = 0
for surface B = -q + 2q - 2q = -q
so A and D have net electric flux = 0
so option E) is the correct answer