What is resistance?
Electrons move through a conductor when electric current flows. All materials impede flow of electric current to some extent. This characteristic is called resistance. Resistance increases with an increase of length or decrease of cross-section of a material. The unit of measurement for resistance is ohms and its symbol is the Greek letter omega (Ω). The resistance of one ohm means a conductor allows a current of one amp to flow with a voltage of one volt. All materials are difference in allowing electrons flow. Materials that allow many electrons to flow freely are called conductors such as copper, silver, aluminium, hydrochloric solution, sulphuric acid and saltwater. In contrast, materials which allow few electrons to flow are called insulators such as plastic, rubber, glass and dry paper. Another type of materials, semiconductors have characteristics of both conductors and insulators. They allow electrons to move while being able to control flow of electrons and examples are carbon, silicon and germanium, etc. The resistance of conductor depends on two main factors as the followings:
1.Types of material
2.Temperature of material