Sound level in room vs. number of people

I am having a little difficulty solving a problem, can you please help? The question is: The sound level in a room of 35 people talking is 63dB. How many people must leave the room to lower the sound level to 57 dB? Assume that all the people are speaking at the same intensity.

A system of point charges

Four charges are placed at the corners of a square, where q is positive. Initially there is no charge in the center of the square. 1) Find the work, W required to bring the charge Qf from infinity and place it at the center of the square. 2) Find the magnitude of the electric force on the charge q when it is placed a ...continues

electron problem

A voltage of 9 V is applied across the ends of a piece of copper wire 11 cm long. Given me = 9.11 x 10-31 kg and qe = -1.6 x 10-19 C. 1) What is the electron's acceleration in m/s2 ? 2) What is the speed of the electron after traveling 4 x 10-11 m, if it does not collide with a copper ion over this distance, in m/s? 3) Wha ...continues

potential problem

An infinite sheet of charge that has a surface charge density of 28 nC/m2 lies in the yz plane, passes through the origin, and is at a potential of 0.8 kV. A long wire having a linear charge density of 116 nC/m lies parallel to the y axis and intersects the x axis at 2m. What is the potential energy of a 3.2 nC charge place ...continues

Electric field

1) Given: V = αx2y2 + βz2(x2 - γ) + δy3z Where α = 5 V/m4, β = 6.6 V/m4, γ = 3.4 m2, and δ = 5.3 V/m4. What is the y component of the electric field Ey at (4.6m, -4 m, 4.7 m)? Answer in units of V/m. 2) The electric potential in a certain region is: ...continues

Energy problem

A charge of 1 µC is distributed uniformly along the circumference of a circle with a radius of 30 cm. How much external energy is required to bring a charge of 61 µC from infinity to the center of the circle? Let ke = 8.98 x 109 nm2/C2. Answer in units of J.

Capacitance problem

When a potential difference of 178 V is applied to the plates of a parallel-plate capacitor, the plates carry a surface charge density of 47nC/cm^2. What is the distance between the plates? Answer in units of micrometers. I know that d = (epsilon * V)/sigma. I think my unit conversion is incorrect.

Equipotential Problem

Additional Problem 1: A hydrogen atom when in its lowest energy state consists of a proton of charge +e and an electron of charge -e and mass 9.1x10-31 kg. In the Bohr model of the atom, the electron moves around the nucleus in a circular orbit of radius 0.51x10-10 m. Determine the speed that another electron, starting very f ...continues

How do you apply the binomial approximation

Consider a dipole consisting of two charged particles on the x axid, one with positive charge q+ located at x=+1/2d and one with negative q- charge located at x=-1/2d a) Derive an exact expression for the three dimensional potential field created by this dipole at a point P whose coordinates are {x,y, and z}...See attachment

Resistance of a wire

A wire with resistance R is lengthened to 2.28 times its original length by pulling it through a small hole. What is the resistance of the wire after it is stretched in units of R.