a measure of how difficult it is for electric current to travel through a material

good conductors (metals) have low resistance, while insulators (plastic, rubber) have relatively high resistance

symbol is R measured in the unit “ohms” which has

the symbol Ω

resistor an electrical device that has a specific resistance value

circuit symbol:

depending on the desired effect in the circuit, different level resistors can be used

if a smooth steady change in current is required, a variable resistor is used

all electrical components in a circuit have electrical resistance

connecting wires and switches generally have low resistance

when charges encounter resistance the energy is usually converted to thermal energy (heat)

this can be a waste (ex: during transmission from power plants) or it can be necessary (ex: incandescent light bulb filaments)

are special materials that have no electrical resistance

current technology can only demonstrate superconductivity at extremely low temperatures

the goal is to reduce wasted thermal energy and create wires that are 100% efficient

ohmmeter a device that measures electrical resistance in a circuit

should be connected in parallel must NOT be used on a live circuit

(turn the power off first!!) symbol for an ohmmeter is: when testing a load with an ohmmeter,

the resistance should read low

there are 4 main factors that affect resistance:1. type of material

conductor vs insulator

2. length of wire longer wire provides more resistance

3. diameter increased thickness will decrease resistance

4. temperature higher temperatures actually increase resistance

the relationship between resistance, current and voltage is summarized in ohm’s law

“the voltage in a conductor is proportional to the current if the temperature remains constant”…so V α I

the equation can be written as:

R = V I

Calculate the resistance of a load with a voltage of 25 V and a current of 410 mA.

61 Ω