resistance
As the free electrons move through the circuit, they encounter atoms that do not readily give up electrons. This opposition to the flow of electrons (the current) is called resistance (r).
Every material offers some resistance or opposition to current flow. The degree of resistance of a material depends on its size, shape, and temperature.
Materials with a low resistance are called conductors. Conductors have many free electrons and offer little resistance to current flow. As previously mentioned, silver, copper, gold, and aluminum are examples of good conductors.
Materials with a high resistance are called insula- tors. Insulators have few free electrons and offer a high resistance to current flow. As previously mentioned, glass, rubber, and plastic are examples of good insulators.
Resistance is measured in ohms, a unit named for the German physicist and mathematician George Simon Ohm (1787–1854). In 1827, Ohm published a paper acknowledging the mathematical relation- ship among current, voltage, and resistance known as Ohm’s law. The symbol for the ohm is the Greek letter omega (Ω).
Questions
1. What is the term used to describe opposition to current flow?
2. What is the main difference between conductors and insulators?
3. What letter is used to represent resistance?
4. What is the symbol used to represent the unit of resistance?
5. What is the unit of resistance?