1. The problem statement, all variables and given/known data The electric field strength just above one face of a copper penny is 2230 N/C. What is the surface charge density on this face of the penny? 2. Relevant equations Electric field of an infinite plane of charge = η/(2*ε0) 3. The attempt at a solution I used the above equation, and the result was 3.95 x 10-8C/m2. However, this is not the correct answer. Where am I going wrong in my thinking? This homework problem comes from the textbook chapter about Gauss's Law, yet I do not see how Gauss's Law can tie into this question.