resistance

Resistance is the opposition a material offers to the flow of electric current.

• Imagine electric current as water flowing through a pipe. A wide, smooth pipe lets water pass easily, while a narrow or rough pipe slows it down. Similarly, a wire with greater resistance makes it harder for electric charges to move through it.
• As charges move through a resistant wire, they bump into the particles of the material. These collisions transfer energy to the wire, making it hot.
• Resistance depends on the wire’s material, length, and thickness. A longer or thinner wire usually has more resistance, while a thicker wire usually has less.
• Materials such as copper have low resistance, so they are useful for connecting wires. Nichrome has higher resistance, so it is useful in heating elements such as those in irons, toasters, and heaters.
• Resistance is useful when heat is needed, but too much resistance in ordinary power cables wastes electrical energy as unwanted heat.