# electric resistance

## is resistance good or bad

Resistance can be helpful or just a drain on electrical energy. If the aim is to transmit electric current through a wire from one place to another, then resistance is a drawback. It reduces the amount of electrical energy that is transmitted because some of the current is absorbed by particles of matter. On the other hand, if the aim is to use electricity to produce heat or light, then resistance is useful. When particles of matter absorb electrical energy, they change it to heat or light. For example, when electric current flows through the tungsten wire inside an incandescent light bulb like the one in the Figure 1.1, the tungsten resists the flow of electric charge. It absorbs electrical energy and converts some of it to light and heat. Q: The tungsten wire inside a light bulb is extremely thin. How does this help it do its job? A: The extremely thin wire has more resistance than a wider wire would. This helps the wire resist electric current and change it to light.

## factors that affect resistance

How much resistance a material has depends on several factors: the type of material, its width, its length, and its temperature. All materials have some resistance, but certain materials resist the flow of electric current more or less than other materials do. Materials such as plastics have high resistance to electric current. They are called electric insulators. Materials such as metals have low resistance to electric current. They are called electric conductors. A wide wire has less resistance than a narrow wire of the same material. Electricity flowing through a wire is like water flowing through a hose. More water can flow through a wide hose than a narrow hose. In a similar way, more current can flow through a wide wire than a narrow wire. A longer wire has more resistance than a shorter wire. Current must travel farther through a longer wire, so there are more chances for it to collide with particles of matter. A cooler wire has less resistance than a warmer wire. Cooler particles have less kinetic energy, so they move more slowly. Therefore, they are less likely to collide with moving electrons in current. Materials called superconductors have virtually no resistance when they are cooled to extremely low temperatures.

## what is resistance

In physics, resistance is opposition to the flow of electric charges in an electric current as it travels through matter. The SI unit for resistance is the ohm. Resistance occurs because moving electrons in current bump into atoms of matter. Resistance reduces the amount of electrical energy that is transferred through matter. Thats because some of the electrical energy is absorbed by the atoms and changed to other forms of energy, such as heat. Q: In the rugby analogy to resistance in physics, what do the players on each team represent? A: The player on the blue and black team represents a moving electron in an electric current. The players on the red and blue team represent particles of matter through which the current is flowing.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

the si unit for electric resistance is the

``````a) amp.

b) watt.

c) volt.

-->  d) ohm.
``````

resistance reduces the amount of electrical energy that is transferred through matter.

``````-->  a. true

b. false
``````

all materials have some electric resistance.

``````-->  a. true

b. false
``````

factors that affect the electric resistance of a wire include the wires

``````a) chemical makeup.

b) length.

c) width.

-->  d) all of the above
``````

a cooler wire has more electric resistance than a warmer wire.

``````a. true

-->  b. false
``````

## diagram questions

No diagram questions associated with this lesson