Voltage/Current/Resistance Circuits:

Most of the direct current (dc) circuits can be boiled down eventually to three major components: a set of conductors, a voltage source, and a resistance. This is shown in the schematic diagram shown below. The voltage of the emf source is termed E (or at times V); the current in the conductor is termed I; the resistance is termed R. The standard units for such components are the volt (V), the ampere (A), and the ohm (?), correspondingly. Note which characters here are italicized and which are not. The italicized characters symbolize mathematical variables; non-italicized characters symbolize symbols for units.

You already know that there is an association among these three quantities. When one of them changes, then one or both of the others will also change. When you make the resistance smaller, the current will get larger. When you make the emf source smaller, the current will reduce. When the current in the circuit rises, the voltage across the resistor will raise. There is a simple arithmetic association among these three quantities.

Figure: A simple dc circuit. The voltage = E, the current = I, and the resistance R.