Resistance in Circuits PDF

# RESISTANCE in CIRCUITS Electrical resistance is the opposition to the movement of electrons as they flow through a circuit. The symbol for resistance is R. The unit for resistance is the ohm (Ω). Electrons can flow through certain materials easier than others. Insulators offer a great deal of res...

# RESISTANCE in CIRCUITS Electrical resistance is the opposition to the movement of electrons as they flow through a circuit. The symbol for resistance is R. The unit for resistance is the ohm (Ω). Electrons can flow through certain materials easier than others. Insulators offer a great deal of resistance to electron flow. Conductors allow the free flow of electrons. ## FACTORS THAT AFFECT RESISTANCE 1. **Type of material** - Metals are the best conductors. Copper, silver and gold are great conductors. 2. **Cross-sectional area** - Thicker wires have less internal resistance than thinner ones. - Electrons flowing through a thicker wire have more room to move freely (ex. #14 wire vs. #20) 3. **Length** - As you increase the length of a wire, its internal resistance increases. - This is because electrons have to travel through more material. - The longer the extension cord, the warmer it will get because of the increased resistance. 4. **Temperature** - Resistance increases with temperature. Atoms are very active and vibrate more in hot objects and this reduces electron flow. ## MEASURING RESISTANCE An ohmmeter is a device designed to measure resistance. It must be connected in parallel just like a voltmeter to measure resistance. # RESISTORS in CIRCUITS A dimmer switch is a typical resistor. A resistor is an electrical device that reduces the current in a circuit. Types of variable resistors are dimmer switches and volume controls. Here is a typical symbol for a resistor in a circuit diagram: ``` ____ | | |----| | | ____ ``` Here is what an actual resistor looks like: - A small cylindrical component with two wires sticking out of it.