# 2018 AP Physics 1 Free Response #2

TLDRIn this educational video, Alan from Bottle Stem Coach tackles a 2018 AP Physics 1 free response question involving conductive dough cylinders. He guides viewers through plotting resistance against L/A (length over cross-sectional area) to determine resistivity, emphasizing the importance of best-fit lines and unit accuracy. Alan also discusses the impact of dough shape on resistivity, concluding it's material-dependent, and suggests an experiment to test resistivity's temperature sensitivity. The video includes a self-assessment based on the scoring guidelines, highlighting the importance of methodical approach and accuracy in scientific experiments.

###### Takeaways

- π¬ Alan discusses a physics experiment involving conductive dough cylinders to determine resistivity.
- π The experiment involves molding dough into cylinders with various cross-sectional areas and lengths.
- β‘ Students apply a potential difference across the dough cylinders to measure their resistance.
- π The resistance is calculated using the formula R = Ο * (L / A), where R is resistance, Ο is resistivity, L is length, and A is cross-sectional area.
- π Alan suggests plotting resistance (R) against L/A to find the slope, which would represent resistivity (Ο).
- π Alan calculates L/A values for different data points to use in the graph.
- π The script includes a step-by-step guide on how to plot the data and perform a linear regression to find the slope.
- π€ The resistivity of the dough is assumed to be uniform regardless of the shape of the dough, as long as the current distribution is uniform.
- π‘οΈ A follow-up experiment is proposed to investigate the effect of temperature on resistivity by heating the dough and measuring resistance at different temperatures.
- π The script outlines the need for a heat lamp, thermometer, and method to measure resistance for the temperature experiment.
- π The video aims to provide a clear explanation and guide for students to replicate the experiment and understand the concept of resistivity.

###### Q & A

### What is the main topic of the video?

-The main topic of the video is solving a physics problem related to determining the resistivity of conductive dough cylinders using AP Physics free response questions from 2018.

### What is the basic equation used to calculate resistance?

-The basic equation used to calculate resistance is R = Ο(L/A), where R is resistance, Ο is resistivity, L is length, and A is cross-sectional area.

### How does the video suggest determining resistivity?

-The video suggests determining resistivity by plotting resistance (R) against L/A, and then finding the slope of the best-fit line, which would represent resistivity (Ο).

### What is the significance of plotting L/A against resistance?

-Plotting L/A against resistance allows for the visualization of the relationship between these variables, making it easier to identify the slope of the line, which is proportional to resistivity.

### What units are used for resistivity in the context of this video?

-The units for resistivity in this context are ohm-meters (Ξ©Β·m).

### Why is it important to be careful with units when calculating resistivity?

-Being careful with units is important to ensure the accuracy of the calculations and to correctly interpret the physical quantities involved in the experiment.

### How does the shape of the conductive material affect the resistivity measurement according to the video?

-The video states that, assuming uniform current distribution, the shape of the conductive material (cylinders or rectangular shapes) does not affect the resistivity measurement.

### What is the proposed method to determine if resistivity depends on the temperature of the dough?

-The proposed method involves heating the dough with a heat lamp, measuring the temperature with a thermometer, and recording the resistance at each temperature to observe changes in resistivity.

### Why is it necessary to control all variables except temperature in the temperature-dependent resistivity experiment?

-Controlling all variables except temperature ensures that any changes in resistance are due to temperature changes, allowing for accurate observation of the relationship between resistivity and temperature.

### What scoring guidelines are mentioned in the video for the experiment?

-The scoring guidelines mentioned include choosing appropriate quantities to graph, labeling axes with units, drawing a linear trend, and controlling variables correctly.

### What did the video creator miss in terms of the scoring guidelines?

-The video creator missed labeling the units directly on the graph axes and possibly underestimated the resistivity value, leading to a slight deviation from the expected result.

###### Outlines

##### π¬ Experiment on Conductive Dough's Resistivity

In this segment, Alan from Bottle Stem, Coach presents an AP Physics problem involving an experiment with conductive dough. Students mold the dough into cylinders with different cross-sectional areas and lengths, apply a potential difference, and measure the resistance. The goal is to determine the resistivity of the dough. Alan suggests plotting resistance against the ratio of length to cross-sectional area to find the slope, which represents resistivity. He calculates the ratio for each cylinder, prepares a graph, and attempts to find the best-fit line to determine the resistivity value.

##### π Analyzing Resistivity and Shape's Impact

Alan discusses whether changing the shape of the dough to a long rectangular form would affect the resistivity. He explains that, theoretically, the resistivity should only depend on the material, assuming uniform current distribution. However, he acknowledges that in real-world scenarios, factors like the size of the dough could influence the results. Alan then moves on to describe an experiment to determine the effect of temperature on resistivity, suggesting the use of a heat lamp and a thermometer to vary and measure the dough's temperature while recording resistance values.

##### π Scoring Guideline and Experiment Procedure

The final paragraph focuses on the scoring guidelines for the experiment and the detailed procedure for an experiment to measure the resistivity's dependence on temperature. Alan outlines the need to control all variables except for temperature, suggests using a heat lamp to vary the dough's temperature, and emphasizes the importance of measuring resistance accurately. He also reflects on his own performance, noting the points he might have missed due to inaccuracies in plotting and estimating the resistivity value from the graph.

###### Mindmap

###### Keywords

##### π‘Conductive Dough

##### π‘Cylinders

##### π‘Potential Difference

##### π‘Resistance

##### π‘Resistivity

##### π‘Best-Fit Line

##### π‘Slope

##### π‘Linear Trend

##### π‘Units

##### π‘Temperature

##### π‘Heat Lamp

###### Highlights

Introduction to the AP Physics free response question from 2018 involving conductive dough cylinders.

Students mold conductive dough into cylinders with various cross-sectional areas and measure resistance.

The basic equation for resistance is derived as R = Ο(L/A), where Ο is resistivity.

Using the slope of a best-fit line to determine resistivity from plotted data.

Calculating L/A values for each data point to prepare for graph plotting.

Setting up the graph with resistance on the Y-axis and L/A on the X-axis.

Plotting the data points and estimating the best-fit straight line.

Determining the slope of the line to find the resistivity of the dough.

The importance of units in calculating resistivity, given as ohms meter.

Discussion on whether changing the shape to a long rectangular shape affects resistivity.

Assumption of uniform current distribution for resistivity measurement.

Proposing an experiment to determine if resistivity depends on dough temperature.

Detailing the experimental setup including a heat lamp and thermometer.

Instructions for heating the dough, measuring temperature and resistance.

Scoring guidelines and self-assessment of the experiment's accuracy and methodology.

Mistakes made in the experiment such as not labeling units correctly on the graph.

Final thoughts on the experiment's steps and a call to action for feedback from viewers.

###### Transcripts

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