High School Physics : Understanding Resistance

Study concepts, example questions & explanations for High School Physics

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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?

Possible Answers:

Resistance would decrease substantially

Resistance would increase substantially

We need to know the numerical values to solve

Resistance would remain unchanged

Correct answer:

Resistance would decrease substantially

Explanation:

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 #2 : Resistors

When current in a circuit crosses a resistor, energy is lost. What form does this lost energy most commonly take?

Possible Answers:

The energy is converted into light

The energy is converted into sound

The energy is converted into heat

The energy is not converted; it simply disappears

The energy is converted into motion

Correct answer:

The energy is converted into heat

Explanation:

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 #21 : Electricity And Magnetism

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?

Possible Answers:

Decreasing the length of the wire

Increasing the diameter of the wire

Decreasing the diameter of the wire

Increasing the length of the wire

None of these

Correct answer:

None of these

Explanation:

The formula for resistance is: 

 

Above,  is length,  is the cross-sectional area of the wire, and  is the resistivity of the material, and is a property of that material. The resistivity is constant for a given material, and thus cannot be changed by altering the dimensions of the wire.

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