2015 AP Physics 1 free response 2 c and d

Khan Academy
10 Apr 201609:51
EducationalLearning
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TLDRThe video script discusses an experiment to determine if a light-bulb is non-ohmic by examining how its resistance changes with varying current. The setup involves a simple series circuit with a variable power source to alter voltage and thus current. The resistance is calculated using Ohm's Law, with voltage across the bulb divided by the current. The experiment requires collecting data on voltage and current at different power source settings and analyzing these to see if the resistance changes, indicating non-ohmic behavior. Uncertainties in measurements from voltmeters and ammeters are considered, emphasizing the importance of instrument sensitivity and the potential for rounding errors to affect the conclusions.

Takeaways
  • 🔍 A light-bulb is considered non-ohmic if its resistance changes with the current.
  • 🔧 The setup from part a can be used to determine the light-bulb's ohmic or non-ohmic behavior by measuring resistance.
  • 📈 Resistance can be calculated using Ohm's Law: Resistance (R) = Voltage (V) / Current (I).
  • 🔄 To observe changes in resistance, the current through the light-bulb needs to be altered.
  • ⚙️ A variable power source can be used to change the voltage across the circuit, which in turn changes the current.
  • 📊 The current in a simple series circuit remains constant, so changing the voltage will affect the current through the light-bulb.
  • 📝 For part c, no modification of the setup is needed; the current can be changed by varying the power source.
  • 🌡️ Additional data to be collected includes the voltage across the bulb and the current entering or exiting the bulb as the power source is varied.
  • 📊 In part d, data analysis involves comparing the calculated resistance at different voltages to determine if the light-bulb is non-ohmic.
  • 🤔 Uncertainties in the voltmeters and ammeters can affect the conclusions, as instrument sensitivity and rounding can lead to aberrant results.
  • 🔎 It's crucial to consider the sensitivity of instruments and the potential impact of measurement rounding on the analysis of experimental data.
Q & A

  • What is the main topic of the script?

    -The main topic of the script is determining whether a light-bulb is non-ohmic by observing how its resistance changes with varying current.

  • What is the definition of a non-ohmic device?

    -A non-ohmic device is one whose resistance changes as a function of the current flowing through it.

  • How can the setup from part a be used to determine the resistance of the light-bulb?

    -The setup from part a can be used by applying Ohm's Law, which states that voltage (V) is equal to current (I) times resistance (R). By measuring the voltage across the light-bulb and the current flowing through it, one can calculate its resistance (R = V/I).

  • How can the current through the light-bulb be changed?

    -The current through the light-bulb can be changed by varying the voltage across the entire circuit using a variable power source. Since the circuit is in series, changing the voltage will result in a change in current.

  • What additional data needs to be collected in part c of the experiment?

    -In part c, one needs to collect the voltage across the light-bulb as the current changes due to the variation in the power source, as well as the current entering and exiting the light-bulb.

  • How can the data be analyzed to determine if the light-bulb is non-ohmic?

    -The data can be analyzed by calculating the resistance of the light-bulb at different voltage levels. If the calculated resistance changes when the voltage (and consequently the current) is altered, the light-bulb is non-ohmic.

  • What is the significance of instrument sensitivity in this experiment?

    -Instrument sensitivity is crucial because it affects the precision of the measurements. The rounding of measurements to the nearest voltage or current value could potentially mask or falsely indicate changes in resistance that are within the sensitivity limits of the voltmeters and ammeters.

  • How might uncertainties in the voltmeters and ammeters affect the conclusions of the experiment?

    -Uncertainties in the voltmeters and ammeters could lead to aberrant results. For instance, a change in resistance might not be detected if it's too small to be registered by the instruments, or the rounding of measurements might falsely suggest a change in resistance when there is none.

  • What is the relationship between voltage and current in a simple series circuit?

    -In a simple series circuit, the voltage drop across each component is proportional to its resistance, and the current flowing through each component is the same, as there is only one path for the current to take.

  • What is the formula to calculate resistance based on the information given in the script?

    -The formula to calculate resistance based on the information in the script is R = V/I, where R is resistance, V is voltage, and I is current.

  • How does the experimenter propose to test for non-ohmic behavior?

    -The experimenter proposes to test for non-ohmic behavior by varying the power source voltage to change the current through the light-bulb and then measuring the voltage across the bulb and the current entering or exiting the bulb at different voltage levels to determine if the resistance changes.

Outlines
00:00
🔬 Experiment Setup and Resistance Measurement

This paragraph discusses the experimental setup required to determine if a light-bulb is non-ohmic. It explains that the setup from part a can be used without modification, as it allows for the measurement of resistance through the formula V=IR, where V is voltage, I is current, and R is resistance. The paragraph emphasizes the need to change the current through the light-bulb and observe how the resistance changes. It suggests using a variable power source to alter the voltage across the circuit, which in turn changes the current. The key points include understanding the relationship between voltage, current, and resistance, and the method to determine if the light-bulb's resistance changes with current.

05:00
📝 Data Collection and Analysis for Non-ohmic Determination

This paragraph focuses on the data that needs to be collected and how to analyze it to conclude whether the light-bulb is non-ohmic. It outlines the process of varying the power source to change the voltage and current, and then measuring the resistance at different levels. The paragraph also discusses the importance of considering the uncertainties in the measurements from voltmeters and ammeters, and how these can affect the conclusion. It highlights the need for caution due to the sensitivity of the instruments and the potential for rounding errors to influence the results. The main points are the methodology for analyzing data, the impact of instrument sensitivity, and the potential for measurement errors to affect the determination of non-ohmic behavior.

Mindmap
Keywords
💡non-ohmic
The term 'non-ohmic' refers to a type of electrical behavior where the resistance of a component changes with the amount of current flowing through it. This is in contrast to ohmic components, where resistance remains constant regardless of the current. In the context of the video, the main theme is to determine whether a light-bulb exhibits non-ohmic behavior by observing if its resistance changes with varying current. The script discusses modifying the setup to test for this characteristic by altering the voltage across the circuit, which in turn changes the current through the light-bulb.
💡resistance
Resistance is a property of a material or component that hinders the flow of electric current. It is a fundamental concept in the study of electronics and is often symbolized by the Greek letter 'R'. In the video, resistance is the key factor being measured to determine if the light-bulb is non-ohmic. The script explains that resistance can be calculated using Ohm's Law, which states that resistance is equal to the voltage divided by the current (R = V/I). The experiment aims to see if the calculated resistance of the light-bulb changes as the current changes, which would indicate non-ohmic behavior.
💡current
Current, measured in amperes (or amps), is the flow of electric charge in a circuit. It is the central quantity being manipulated in the experiment described in the video, as the goal is to determine how the resistance of the light-bulb changes with varying levels of current. The script outlines a method for changing the current by adjusting the voltage provided by a variable power source, which in turn affects the current flowing through the light-bulb. By measuring the voltage and current before and after the change, the resistance of the light-bulb can be calculated and analyzed to identify any non-ohmic behavior.
💡voltage
Voltage, also known as electric potential difference, is the force that drives electric charge through a circuit and is measured in volts. In the context of the video, voltage plays a crucial role in the experiment as it is used to alter the current flowing through the light-bulb. By changing the voltage across the circuit using a variable power source, the script explains that the current through the light-bulb will also change, allowing for the measurement of resistance at different current levels and the determination of whether the light-bulb is non-ohmic.
💡Ohm's Law
Ohm's Law is a fundamental principle in electrical engineering that states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance between them, often expressed as V = IR. In the video, Ohm's Law is used to calculate the resistance of the light-bulb by measuring the voltage across it and the current flowing through it. The law is essential for understanding the relationship between voltage, current, and resistance and is the basis for the experiment to determine the ohmic or non-ohmic nature of the light-bulb.
💡variable power source
A variable power source is a device that provides a controlled and adjustable voltage or current to a circuit. In the video, the variable power source is used to change the voltage across the circuit, which in turn changes the current flowing through the light-bulb. This is a critical component of the experimental setup, as it allows for the systematic variation of current to test for non-ohmic behavior in the light-bulb. By adjusting the power source, the experimenter can measure how the resistance of the light-bulb changes with different levels of current.
💡voltmeters
Voltmeters are instruments used to measure and indicate the voltage difference between two points in an electrical circuit. In the context of the video, voltmeters are essential for measuring the voltage across the light-bulb at different current levels. These measurements, in conjunction with current measurements from an ammeter, are used to calculate the resistance of the light-bulb and to analyze its behavior. The script also discusses the importance of considering the uncertainties and sensitivities of voltmeters in the experimental results, as these can affect the accuracy of the conclusions drawn about the light-bulb's resistance.
💡ammeters
Am meters, or ammeters, are instruments designed to measure the current flowing through a circuit. In the video, an ammeter is used to measure the current entering or exiting the light-bulb. These measurements, along with voltage readings from a voltmeter, are necessary to calculate the resistance using Ohm's Law. The script highlights the need to be aware of the sensitivities and potential rounding errors of ammeters, as these can influence the precision of the experimental data and the determination of whether the light-bulb exhibits non-ohmic characteristics.
💡uncertainties
Uncertainties in the context of the video refer to the potential errors or variations in the measurements taken by the instruments, such as voltmeters and ammeters. These uncertainties can arise from the sensitivity of the instruments, rounding of readings, and other factors that may affect the precision of the data. The script emphasizes the importance of considering these uncertainties when analyzing the experimental data to determine the nature of the light-bulb's resistance. Understanding and accounting for these uncertainties are crucial for drawing accurate and reliable conclusions from the experiment.
💡sensitivity
Sensitivity in the context of the video pertains to the ability of measuring instruments, like voltmeters and ammeters, to detect small changes in the quantities they measure. The script discusses the need to be mindful of the sensitivity of these instruments when conducting the experiment, as it can impact the observed results and the determination of whether the light-bulb is non-ohmic. For instance, if the sensitivity is not high enough, it may not register small changes in resistance that actually occur, leading to potentially incorrect conclusions about the light-bulb's behavior.
💡data analysis
Data analysis involves the process of examining, cleaning, transforming, and modeling data to draw conclusions or make decisions. In the video, data analysis is crucial for determining the nature of the light-bulb's resistance. The script outlines a method for analyzing the collected data by comparing the calculated resistance at different current levels and considering the impact of instrument uncertainties. Proper data analysis ensures that the conclusions about the light-bulb being ohmic or non-ohmic are based on accurate and reliable information.
💡experimental setup
The experimental setup refers to the arrangement of equipment and procedures used to conduct an experiment. In the video, the setup involves a circuit with a light-bulb and instruments to measure voltage and current. The script describes how the setup may need to be modified, such as by incorporating a variable power source, to systematically change the current through the light-bulb and measure its resistance. The design of the experimental setup is critical for accurately testing the light-bulb's behavior and obtaining reliable data for analysis.
Highlights

The problem discussed involves determining whether a light-bulb is non-ohmic by observing if its resistance changes with current.

The setup from part a can be used or modified to determine the light-bulb's resistance characteristics.

To measure resistance, the formula V=IR (voltage equals current times resistance) can be utilized.

The current through the light-bulb can be changed by adjusting the voltage across the entire circuit.

The circuit is simple and in series, meaning the current is consistent throughout.

Measuring voltage (V) and current (I) allows for the calculation of the light-bulb's resistance (R).

No modification to the setup is necessary for the initial part of the experiment.

By varying the power source, the resistance of the bulb can be measured as the current changes.

The first part of the experiment confirms that the number of electrons per second entering and exiting the bulb is the same.

For part d of the experiment, data analysis involves comparing resistance calculated from different voltages and currents.

The equality of V/I ratios after changing the voltage and current will indicate if the bulb is ohmic or non-ohmic.

Uncertainties in voltmeters and ammeters can affect the conclusions drawn about the resistance being non-ohmic.

Instrument sensitivity and rounding in measurements can lead to aberrant results or fail to register small changes.

Care must be taken to account for the sensitivity of instruments when conducting scientific experiments.

Rounding to the nearest 0.1 volt or 0.01 amp can result in perceived differences in V over I when none exist or vice versa.

The experiment aims to determine if the light-bulb's resistance changes with current, which would indicate it is non-ohmic.

Adjusting the power source is a method to change the current through the light-bulb for the experiment.

Measuring both voltage across and current entering/exiting the bulb is essential for determining its resistance.

Transcripts

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