Direct Current: EMF, Ohm's Law for the Complete Circuit and Connections
What keeps charge flowing around a closed loop, and how to predict every current and voltage in it
Big Idea: A steady direct current (DC) is a continuous, one-directional flow of charge around a closed circuit. The flow does not start by itself: a source (a battery, a cell, a generator at Toktogul) does work to push charge through itself against internal forces. The energy the source gives to each coulomb of charge is its electromotive force (EMF), and the whole current is fixed by Ohm's law for the complete circuit: I = ε / (R + r).
By the end you will be able to:
- define current, EMF and internal resistance with correct SI units,
- apply Ohm's law both for a section and for the complete circuit,
- combine resistors in series and in parallel,
- compute electrical work, power and the Joule-Lenz heat,
- explain why terminal voltage drops when a battery delivers current and how resistance changes with temperature.