In Chapter 3 , we computed electric fields due to several static charge distributions. We next want to consider the situation where charges are moving with a uniform velocity. Such a situation is called a steady current, and fields that arise due to steady currents are static magnetic fields (to be discussed in Chapter 5 ). In this chapter, we first discuss types of currents in Sect. 4.1 and the continuity equation in Sect. 4.2. Then, we discuss currents that arise in conductors in Sect. 4.3. Due to collisions among charges that occur inside a conductor, the resistance of a conductor is introduced as a quantity that represents these collisions. We compute the resistance for several configurations of conductors in Sect. 4.4.