# Physics net charge homework help

1. Nov 3, 2004

### Mild

I've been behind in class. It'd really be helpful if anyone could help me. It's hard, but if you know it, just help me, please. Here it is:
1) Calculate the net charge on a substance consisting of (a) 5 x 10^14 electrons and (b) a combination of 7 x 10^13 protons and 4 x 10^13 electrons.

2) Two identical conducting spheres are placed a distance of 0.3 m between their centers. One is given a charge of 12 x 10^-9 C and the other a charge of -18 x 10^-9 C. (a) Find the electrostatic force exerted on one sphere by the other. (b) The spheres are now connected by a conducting wire. After equilibrium has occurred, find the electrostatic force between the two.

3) The electric force on a point charge of 5 x 10^-9 C at some point is 3.8 x 10^-3 N in the positive X direction. What is the magnitude of the electric field at this location?

4) What are the magnitude and direction of the electric field setup by the proton at the position of the electron in the hydrogen atom?

5) The electrons in a particle beam each have a kinetic energy of 1.6 x 10^-17 J. What are the magnitude and direction of the electric field that will stop these electrons in a distance of 10cm?

6) A proton accelerates from rest in a uniform electric field of 640 N/C. At some later time, its speed is 1.20 x 10^6 m/s. (a) Find the acceleration of the proton. (b) How long does it take the proton to reach this velocity? (c)How far has it moved in this time? (d) What is its kinetic energy at this time?

7) (a) How much work is done by a uniform electric field 200 N/C as the charge moves a distance of 2 cm in the field? (b) What's the difference in potential energy between these two points?

8) Show that units N/C and V/m are equivalent.

9) The difference in potential energy between the accelerating plates of a TV set is about 25,000 V. If the distance between these plates is 1.5 cm, find the magnitude of the uniform electric field in this region.

10) (a) What potential difference is needed to stop an electron with an initial speed of 4.2 x 10^5 m/s? (b)How much energy does this require?

11) At what distance from a point charge of 6 microcoulombs would the potential equal 27,000 V?

12) Calculate the speed of (a) an electron that has a kinetic energy of lev, and (b) a proton that has a kinetic energy of 1eV.

13) How much energy is gained by a charge of 75 microcoulombs moving through a potential difference of 90V? Express your answer in (a) joules and (b) electronvolts.

2. Nov 3, 2004