Session 3
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Jacob R
Phys 222
Prozorov
9-8-13
Review:
- Explain, in your own words, what flux is?
- How could there be no net electric flux through a closed surface?
- Compare the net flux through a closed surface to the net flux through a closed surface with the
dimensions doubled.
- How would you calculate the flux through a surface that is not perpendicular to the electric
field?
- State Gauss’s law and explain what it means.
Problems:
1. A flat sheet of paper of area 0.250 m2 is oriented so that the normal to the sheet is at an angle
of 60° to a uniform electric field of magnitude 14 N/C. (a) Find the magnitude of the electric flux
through the sheet. (b) For what angle θ between the normal and the electric field is the magnitude
of the flux through the sheet (i) largest and (ii) smallest?
2. You measure an electric field of 1.25 (106) N/C at a distance of 0.150 m from a point charge.
There is no other source of electric field in the region other than this point charge. (a) What is the
electric flux through the surface of a sphere that has this charge at its center and that has radius
0.150 m? (b) What is the magnitude of this charge?
3. A charged paint is spread in a very thin uniform layer over the surface of a plastic sphere of
diameter 12.0 cm, giving it a charge of -35.0 µC. Find the electric field (a) just inside the paint
later; (b) just outside the paint later; (c) 5.00 cm outside the surface of the paint layer.
4. A small sphere with a mass of 4.00 (10-6) kg and carrying a charge of 5.00 (10-8) C hangs from
a thread near a very large, charged insulating sheet, as shown in the figure. The charge density on
the surface of the sheet is uniform and equal to 2.50 (10-9) C/m2. Find the angle of the thread.
Supplemental Instruction
1060 Hixson-Lied Student Success Center  294-6624  www.si.iastate.edu