High School Physics : Understanding Resistance
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Example Questions
Example Question #1 : Understanding Resistance
An electric circuit is set up in series with five resistors. If the resistors remain the same, but the circuit is now set up with the resistors in parallel, how would this affect the total resistance?
Resistance would increase substantially
Resistance would remain unchanged
We need to know the numerical values to solve
Resistance would decrease substantially
Resistance would decrease substantially
Think of resistors as doors, preventing the flow of people (electrons). Imagine the following scenarios: a large group of people are in a room and all try to leave at once. If the five resistors are in series, that's like having all of these people trying to go through all five doors before they can leave. In a circuit, all the electrons in the current mast pass through every resistor.
If the resistors are in parallel, it's like having five separate doors from the room. All of a sudden, the group can leave MUCH faster, encountering less resistance to their flow out of the room. The path of the electrons can split, allowing each particle to pass through only one resistor.
From a formula perspective, the resistors in series are simply summed together to find the equivalent resistance.
In parallel, however, the reciprocals are summed to find the reciprocal equivalent resistance.
Adding whole numbers will always give you a much greater result than adding fractions. For the exact same set of resistors, arrangement in series will have a greater total resistance than arrangement in parallel.
Example Question #1 : Understanding Resistance
When current in a circuit crosses a resistor, energy is lost. What form does this lost energy most commonly take?
The energy is converted into motion
The energy is converted into sound
The energy is converted into heat
The energy is converted into light
The energy is not converted; it simply disappears
The energy is converted into heat
In basic resistors, energy lost due to resistance is converted into heat. In some cases, other conversions also take place (such as generation of light in a lightbulb), but heat is still dissipated along with any alternative conversations. Lightbulbs, batteries, and other types of resistors will become hot as current passes through them.
Example Question #3 : Understanding Resistance
You have a 1m long, 0.5cm diameter copper wire that has an electric current running through it. Which of the following would decrease the wire's overall resistivity?
Increasing the diameter of the wire
Decreasing the length of the wire
None of these
Decreasing the diameter of the wire
Increasing the length of the wire
None of these
The formula for resistance is:
Above, 
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