/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 63 As a research scientist at a lin... [FREE SOLUTION] | 91Ó°ÊÓ

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As a research scientist at a linear accelerator, you are studying an unstable particle. You measure its mean lifetime \(\Delta t\) as a function of the particle's speed relative to your laboratory equipment. You record the speed of the particle \(u\) as a fraction of the speed of light in vacuum \(c .\) The table gives the results of your measurements. $$ \begin{array}{l|lllllll} u / c & 0.70 & 0.80 & 0.85 & 0.88 & 0.90 & 0.92 & 0.94 \\ \hline \Delta t\left(10^{-8} \mathrm{~s}\right) & 3.57 & 4.41 & 5.02 & 5.47 & 6.05 & 6.58 & 7.62 \end{array} $$ (a) Your team leader suggests that if you plot your data as \((\Delta t)^{2}\) versus \(\left(1-u^{2} / c^{2}\right)^{-1},\) the data points will be fit well by a straight line. Construct this graph and verify the team leader's prediction. Use the best-fit straight line to your data to calculate the mean lifetime of the particle in its rest frame. (b) What is the speed of the particle relative to your lab equipment (expressed as \(u / c\) ) if the lifetime that you measure is four times its rest-frame lifetime?

Short Answer

Expert verified
After linear regression, the slope will give you the mean lifetime of the particle in rest frame as \(\tau\). The speed of the particle relative to your lab equipment if the lifetime that you measure is four times is obtained by solving the mentioned equation which will give \(u/c\) as a fraction.

Step by step solution

01

Plotting the graph

First, square the lifetime data to get \( (\Delta t )^2 \) and calculate \( \left(1 - \frac{u^2}{c^2} \right)^{-1} \). The obtained values are to be used as the y and x coordinates respectively of each data point on your plot. Remember, \( c \) is the speed of light and \( u \) is the speed of the particle and have similar units.
02

Perform Linear Regression

Draw the best-fit straight line through the data points. Using the slope of this line, calculate the mean lifetime in the rest frame (\( \tau \)). Since the slope of the line is \( \tau^2 \), you need to take the square root of the slope to get \( \tau \). This linear regression can be done with software like Excel, Google Sheets, or a scientific calculator that supports linear regression.
03

Calculate the Relative Speed

After obtaining \( \tau \) , calculate its speed (\( u \)) when the observed lifetime (\( \Delta t \)) is four times the rest time. By solving the equation \( 4\tau = \gamma \tau \) for \( \frac{u}{c} = \sqrt{ 1 - \left(\frac{\tau}{4\tau}\right)^2 }\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Time Dilation
Time dilation is a fascinating concept derived from Einstein's theory of relativity. It describes how time passes at different rates depending on the relative speed of an observer. In simpler terms, the faster you move, the slower time seems to pass for you relative to someone who is stationary.

In physics, especially relativistic physics, time dilation is crucial for understanding experiments involving particles moving at significant fractions of the speed of light. According to the formula for time dilation, the dilated time \[ \Delta t = \gamma \tau, \]where \( \tau \) is the proper time (or rest lifetime), and \( \gamma \) (gamma) is the Lorentz factor. The Lorentz factor is defined as: \[ \gamma = \frac{1}{\sqrt{1 - \frac{u^2}{c^2}}}. \]This factor accounts for the observed increase in the particle’s lifetime as its speed approaches the speed of light.

This exercise demonstrates how you can use time dilation to calculate how long a particle would live if it were at rest, using data collected from experiments where the particle is moving rapidly relative to the laboratory equipment. By plotting and analyzing the given data, students can practice applying the principles of time dilation to real experimental scenarios.
Linear Regression
Linear regression is a statistical tool to determine the relationship between variables by fitting them to a straight line. It allows you to predict values and identify trends by calculating the best-fit line through a set of data points.

In this exercise, linear regression is applied to plot the squared lifetime of particles \((\Delta t)^2\) against the function \((1 - \frac{u^2}{c^2})^{-1}\). This relationship is expected to be linear due to the transformation based on relativity equations.

To perform linear regression, you can use various tools like Excel, Google Sheets, or other software that supports statistical analysis. Essentially, you calculate the slope (\(m\)) and intercept (\(b\)) of the line:\[ y = mx + b. \]

Here, the slope \(m\) directly provides insight into the mean lifetime of particles in their rest frame, \(\tau\), since it is related as \(\tau^2\). By taking the square root of the slope, one can find the actual rest frame lifetime, gaining valuable understanding of particle behaviors in high-speed experiments.
Experimental Data Analysis
Experimental data analysis involves interpreting data from experiments to test hypotheses and draw conclusions. In the context of this exercise, you begin by calculating necessary transformations of your raw data, such as squaring lifetimes and finding the inverse of a derived function of speed fractional values.

The analysis starts by plotting this transformed data to observe patterns or linear relationships, as suggested by prior theories. Analyzing your graph's linear fit is instrumental in determining if your experimental outcomes align with theoretical predictions or models, like those provided by relativistic physics.

Also, while examining the graph, some key steps include:
  • Ensuring data accuracy and handling any outliers which may skew results.
  • Understanding how the variables relate within the context of the studied phenomenon.
  • Interpreting the slope analytically, as it offers physical meaning in terms of parameters like particle lifetime.
Through this detailed analysis, students not only understand the particular experiment but also gain skills necessary for broader applications in scientific research.

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Most popular questions from this chapter

A particle has rest mass \(6.64 \times 10^{-27} \mathrm{~kg}\) and momentum \(2.10 \times 10^{-18} \mathrm{~kg} \cdot \mathrm{m} / \mathrm{s} .\) (a) What is the total energy (kinetic plus rest energy) of the particle? (b) What is the kinetic energy of the particle? (c) What is the ratio of the kinetic energy to the rest energy of the particle?

Many of the stars in the sky are actually binary stars, in which two stars orbit about their common center of mass. If the orbital speeds of the stars are high enough, the motion of the stars can be detected by the Doppler shifts of the light they emit. Stars for which this is the case are called spectroscopic binary stars. Figure \(\mathbf{P 3 7 . 6 8}\) shows the simplest case of a spectroscopic binary star: two identical stars, each with mass \(m,\) orbiting their center of mass in a circle of radius \(R .\) The plane of the stars' orbits is edge-on to the line of sight of an observer on the earth. (a) The light produced by heated hydrogen gas in a laboratory on the earth has a frequency of \(4.568110 \times 10^{14} \mathrm{~Hz}\) In the light received from the stars by a telescope on the earth, hydrogen light is observed to vary in frequency between \(4.567710 \times 10^{14} \mathrm{~Hz}\) and \(4.568910 \times 10^{14} \mathrm{~Hz}\). Determine whether the binary star system as a whole is moving toward or away from the earth, the speed of this motion, and the orbital speeds of the stars. (Hint: The speeds involved are much less than \(c,\) so you may use the approximate result \(\Delta f / f=u / c\) given in Section \(37.6 .\) ) (b) The light from each star in the binary system varies from its maximum frequency to its minimum frequency and back again in 11.0 days. Determine the orbital radius \(R\) and the mass \(m\) of each star. Give your answer for \(m\) in kilograms and as a multiple of the mass of the sun, \(1.99 \times 10^{30} \mathrm{~kg} .\) Compare the value of \(R\) to the distance from the earth to the sun, \(1.50 \times 10^{11} \mathrm{~m}\). (This technique is actually used in astronomy to determine the masses of stars. In practice, the problem is more complicated because the two stars in a binary system are usually not identical, the orbits are usually not circular, and the plane of the orbits is usually tilted with respect to the line of sight from the earth.)

Two events are observed in a frame of reference \(S\) to occur at the same space point, the second occurring \(1.80 \mathrm{~s}\) after the first. In a frame \(S^{\prime}\) moving relative to \(S\), the second event is observed to occur \(2.15 \mathrm{~s}\) after the first. What is the difference between the positions of the two events as measured in \(S^{\prime} ?\)

A spaceship moving at constant speed \(u\) relative to us broad. casts a radio signal at constant frequency \(f_{0}\). As the spaceship approaches us, we receive a higher frequency \(f\); after it has passed, we receive a lower frequency. (a) As the spaceship passes by, so it is instantaneously moving neither toward nor away from us, show that the frequency we receive is not \(f_{0},\) and derive an expression for the frequency we do receive. Is the frequency we receive higher or lower than \(f_{0} ?\) (Hint: In this case, successive wave crests move the same distance to the observer and so they have the same transit time. Thus \(f\) equals \(1 / T .\) Use the dilation formula to relate the periods in the stationary and moving frames.) (b) A spaceship emits electromagnetic waves of frequency \(f_{0}=345 \mathrm{MHz}\) as measured in a frame moving with the ship. The spaceship is moving at a constant speed \(0.758 c\) relative to us. What frequency \(f\) do we receive when the spaceship is approaching us? When it is moving away? In each case what is the shift in frequency, \(f-f_{0} ?\) (c) Use the result of part (a) to calculate the frequency \(f\) and the frequency shift \(\left(f-f_{0}\right)\) we receive at the instant that the ship passes by us. How does the shift in frequency calculated here compare to the shifts calculated in part (b)?

A baseball coach uses a radar device to measure the speed of an approaching pitched baseball. This device sends out electromagnetic waves with frequency \(f_{0}\) and then measures the shift in frequency \(\Delta f\) of the waves reflected from the moving baseball. If the fractional frequency shift produced by a baseball is \(\Delta f / f_{0}=2.86 \times 10^{-7},\) what is the baseball's speed in \(\mathrm{km} / \mathrm{h} ?\) (Hint: Are the waves Doppler- shifted a second time when reflected off the ball?)

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