- Http Www Thephysicsaviary Com Physics Programs Labs Half Lifelab Index Html 1 (37.9 KiB) Viewed 11 times
- Http Www Thephysicsaviary Com Physics Programs Labs Half Lifelab Index Html 2 (28.73 KiB) Viewed 11 times
- Http Www Thephysicsaviary Com Physics Programs Labs Half Lifelab Index Html 3 (30.97 KiB) Viewed 11 times
- Http Www Thephysicsaviary Com Physics Programs Labs Half Lifelab Index Html 4 (13.85 KiB) Viewed 11 times
- Http Www Thephysicsaviary Com Physics Programs Labs Half Lifelab Index Html 5 (31.21 KiB) Viewed 11 times
- Http Www Thephysicsaviary Com Physics Programs Labs Half Lifelab Index Html 6 (93.68 KiB) Viewed 11 times
- Http Www Thephysicsaviary Com Physics Programs Labs Half Lifelab Index Html 7 (56.97 KiB) Viewed 11 times
- Http Www Thephysicsaviary Com Physics Programs Labs Half Lifelab Index Html 8 (65.03 KiB) Viewed 11 times
2. Attach Excel Plot for In (N) vs. t below. Answer question below the graph: Equation of the line: In (N) - 3. Slope of the line Half-life, ty=0.693/7.- 4. Attach Excel Plot for N vs. t below. Answer question below the graph: Eq. of the fit: N(t)= 2. = 5. Half-life, t'12- (from step 3) λ = % difference= (from step 4)
Table 2 Temperature Difference as a Function of Time Reading Temp. T (°C) Time, t (min) Temp. diff. T (°C) # 0 1 Slope 2 3 4 5 6 7 8 10 20 30 40 50 60 70 Room temperature, TR - 25° C Analysis and Sample Calculation (Part II): 1. T'=T-TR= 2. Attach the Excel semi-log plot below. Answer question under the graph:
3. Time constant + = 4. Half-life, t1/2 = 0.693/2= 5. Half-life, t1/2 = Post Lab Questions: 1. 2. 3. Conclusion: Eq. of line: % difference =
PROCEDURE: PARTI 1. Click on the link below to open the simulation Half-Life Lab and push Begin. http://www.thephysicsaviary.com/Physics ... index.html 2. The experiment starts as soon as you select an Initial Activity by clicking on the upper left box. Select 300.0 decays/s for your sample - it may take several attempts. The clock (Total Time) cannot be interrupted once the sample is selected. Read ahead and 3. The COUNTER starts collecting data from Time t = 0.0 s. You will try to stop counting at t = 10.0 s by pressing the Hold button. [Place your mouse arrow on the Hold button and wait
for the Sample Time to reach 10.0 s.] The Total Time clock will continue to run, but Sample Time At will stop and display the actual duration of counter reading. Record the count N and Sample Time At against Total Time t = 0.0 s in Table 1 in your lab report. 4. For your next reading, wait until Total Time t reaches 60.0 s and immediately click the Reset button to start the count. Wait for Sample Time At to reach 10.0 s (as before) and press the Hold button to stop counting. Record At and the count N against Total Time t = 60.0 s. 5. Continue taking readings at 60.0 s intervals until 10 sets of data are collected. The At value is recorded to note any deviation from the proposed Sample Time of 10.0 s due to your reaction time. Such deviation may account for any discrepancy in your result. ANALYSIS: PART I 1. Calculate In (N) and enter in the designated column on Table 1. Show a sample calculation. 2. Use Excel to plot a ln (N) vs. t plot on a linear graph. Time t will be along the horizontal axis and In (N) along the vertical. Follow the notes on Excel from Lab 1 to obtain the equation for the best fit line. Affix a copy of the graph to the report. Write down the equation relating In (N) to time t underneath the graph. 3. What is the slope of the best fit line? Using λ = - slope and t₁/2 = , from Eq. (4), calculate the half-life t of the radioactive decay of element Bi-211. 0.693 2 4. Use Excel to plot N vs. t on a linear graph paper and use an exponential fit to obtain an equation in the form: N(t) = No e. Affix a copy of the graph to the report. Write the exponential equation for N underneath the graph. Does the λ from step 3 above agree with that from step 4? What is the % difference between the two? 5. The half-life can also be obtained from a N vs. t graph (from step 4 above) as the time when N(t) = ½/2 No; we use the symbol t'1/2 for this value of half-life. Note the value of No, which is the initial count at t = 0. Read from the horizontal axis the time when N reduces to ½/2 No; Record value t'ı/2. Calculate the percentage difference between t1/2 (from step 4) and t'1/2.
PROCEDURE: PART II 1. Here, you will use the simulation Newton's Law of Cooling to heat a container to 100° C and graph the temperature drop as a function of time as the container cools by losing heat to its surroundings. From an analysis of the data, you will determine the half-life of cooling. http://htv-au.vlabs.ac.in/heat-thermodynamics/Newtons Law of Cooling/experiment.html 2. Click on the START EXPERIMENT button. Select material (copper) of the container. Take note of the room temperature (25° C). Click on START HEATING button to attain 100°C. 3. Click on the STOP HEATING button and the computer will generate a Temperature vs. time plot as the container cools (at a faster-than-real-time pace, to save you some time.) 4. Record in your data sheet the room temperature, TR, from the initial reading of the thermometer (see step 2). This will be needed when you compute relative temperature T'. 5. Read and record the temperature values from the computer-generated plot every 10 minutes (place the cursor arrow on the curve to get exact values) over a 70 min interval. You will have T 100° C as your starting temperature at t = 0.
ANALYSIS: PART II 1. After you have completed recording your data for this part, calculate temperature difference, T = T-TR, and record it in the column provided. 2. Use Excel to plot T vs. t on a semi log graph paper (choose vertical axis as logarithmic). This should yield a straight-line fit. Have the equation for the line on the graph. Affix the graph to your report. Record the slope (= -A) of the line under the plot. 3. Calculate the time constant, t, for cooling of the hot object [see Eq. (5)]. Write the equation for your line that contain the values of slope (-2) and intercept (To') [see Eq. (12)]. 4. Use your calculated value of the time constant from step 2 to determine half-life, the time it takes for T' to reach one-half of T'o. This can be calculated using Eq. (4): t1/2 = (In2)/λ. 5. The half-life can also be obtained from the graph directly: find the point on your graph that is on the best fit line and where T'= ½ To. Read the time coordinate where this occurred; call this value of half-life t'12. Calculate the % difference between t1/2 and t'1/2. POST LAB QUESTIONS 1. From Part I, which method of determining half-life is more accurate (t½ or t')? 2. What fraction of an original sample's number of isotopes remains after two half-lives? 3. Does the computer-generated graph for T vs. t in Part II follow exponential behavior? Explain.