Physics 1140 Experimental Physics 1 Debbie Jin Lecture 1: Introduc>on to Course Measurement Uncertainty Standard Format 1 General Informa>on Lecture instructor: Debbie Jin email: [email protected] office hours: Tuesday 11 am-­‐12 pm in the Physics HelpRoom (G2B90) or by appointment Course Website: hTp://www.colorado.edu/physics/phys1140 Textbook: Taylor, An Introduc+on to Error Analysis 2 This week’s reading: Ch. 1 Before next lecture: Ch. 2, Sec. 1-­‐4, 6-­‐7 Important: No lecture next week (for both Mon and Tues classes) 3 Experimental Physics Physics: Discovering fundamental physical laws that govern the natural world through experiments, measurements, and quan>ta>ve analysis. Experiments: 1.  Make quan>ta>ve measurements. (Take data) 2.  Compare with expecta>on. (Analyze data) 3.  Make a conclusion. (Present results) 4 Experimental Physics Physics: Discovering fundamental physical laws that govern the natural world through experiments, measurements, and quan>ta>ve analysis. Experiments that agree with expecta>ons can extend our knowledge by going to new regimes in energy, temperature, precision, size, complexity, etc.
Experiments that disagree with expecta>ons can result in exci>ng discoveries. 5 Examples: Gravity Galileo, in 1589, dropped two masses to see if heavier objects fall faster. The results disproved Aristotle’s theory. image from hTp://demonstra>ons.wolfram.com/ 6 Examples: Quantum Mechanics Hertz, in 1887, did experiments on the photoelectric effect and found results that did not match theory. This resulted in Einstein, in 1905, figuring out that light behaves like a par>cle (photons). Einstein received the 1921 Nobel Prize for “his discovery of the law for the photoelectric effect”. image from hTp://www.sciencetech.technomuses.ca/ 7 Examples: Superconduc>vity Resistance (Ohms) Onnes, in 1911, cooled Hg to very low temperatures (4 Kelvin) and discovered superconduc>vity. Temperature (Kelvin) historic plot from Onnes experiment 1911 8 Examples: Higgs Boson In 2012, experiments at CERN’s Large Hadron Collider saw the first evidence for a new par>cle called the Higgs boson. Theorists Englert and Higgs received the Nobel Prize in 2013. plot from paper in Physics LeTers B, Sept 2012 9 Clicker Ques>on 1 1.  Does your clicker work? A. 
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Yes! What is a clicker? I forgot my clicker. I don’t know. I can’t answer because I don’t have a clicker! 10 Clicker Ques>on 1 1.  Does your clicker work? A. 
B. 
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Yes! What is a clicker? I forgot my clicker. I don’t know. I can’t answer because I don’t have a clicker! 11 Clicker Ques>on 2 •  Any experimental result that disagrees with theory is likely to lead to a new discovery in physics. A.  True B.  False 12 Clicker Ques>on 2 •  Any experimental result that disagrees with theory is likely to lead to a new discovery in physics. A.  True B.  False 13 Clicker Ques>on 3 •  Any experimental result that agrees with theory does not advance science. A.  True B.  False 14 Clicker Ques>on 3 •  Any experimental result that agrees with theory does not advance science. A.  True B.  False 15 What do you get to do in Physics 1140? •  Perform 6 experiments –  in your lab sec>ons •  Learn how to deal with measurement uncertainty (or “error”) –  focus of the lectures and homework –  put into prac>ce in the lab sec>ons •  Learn to make meaningful measurements, draw conclusions, and present results 16 What you will not get to do in Physics 1140 •  Design your own experiments •  Make breakthrough physics discoveries •  Take a final exam that cer>fies you as an experimental physicist • 
Why not? This is a 1 unit introductory physics lab class. 17 Format of Physics 1140 •  Coursework is “frontloaded.” More work at beginning, but all work is done well before finals week •  Weekly 2 hour lab session –  Lab work in G2B66 –  Expect to spend some >me outside lab session to prepare for the lab (pre-­‐lab) and comple>ng your writeup –  First week: Tutorial for Mathema>ca –  Then: 6 labs over 12 weeks •  5 lectures, weekly –  Mon or Tues 4-­‐5 pm –  Homework due Friday by 5 pm, in G2B66 18 Grading •  The course consists of three components: 1.  Clicker ques>ons, HW, plus two online surveys (20% of the total grade). 2.  The prelab ques>ons (20% of total grade). 3.  The lab report (60% of total grade). • Your 6 labs are chosen from a total of 15 labs: –  Lab 1: Lab M1 on the Simple Pendulum –  Lab 2: Choice of M2-­‐6 –  Lab 3: Lab E1 on Circuits –  Lab 4: Choice of E2-­‐5 –  Lab 5: Choice of O1-­‐5. –  Lab 6: Choice of M2-­‐6, E2-­‐5, O1-­‐5 19 Lab books and lab report •  We supply your lab books –  Raw data sheets will stay in the lab, signed by TA •  Guidelines for lab report –  Guidelines and Rubric are posted on website –  Sample lab reports posted in the lab –  Talk to your TA! 20 Deadlines •  Homework due Friday 5:00 pm –  late homework: 0 score •  Prelabs due before you begin a lab –  late prelabs: -­‐50% •  Lab report due 5:00 pm, two working days aqer second lab session for the lab. –  late lab reports: -­‐10% per day •  All materials to be turned in to G2B66 box for your TA. 21 PER Survey •  CU’s Physics Education Research (PER) group
is doing research on how to improve lab classes
•  2% of total grade
-  Complete the first survey by Friday
-  link is on the Physics 1140 website
-  Complete the second survey in week 13
22 All measurements have uncertainty length = 10 cm length = 5.32 cm 23 Repor>ng a measurement length = 10 ± 3 cm “probably between 7 cm and 13 cm” length = 5.32 ± 0.01 cm “probably between 5.31 cm and 5.33 cm” Two ways to es>mate uncertainty: 1.  Think about the measurement technique and equipment. 2.  Look at the scaTer in repeated measurements. 24 Repor>ng a measurement length = 10 ± 3 cm length = 5.32 ± 0.01 cm Standard format 1.  value 2.  uncertainty 3.  units (significant figures) We’ll talk about this later. 25 Why is this important? Standard format 1.  value 2.  uncertainty 3.  units (significant figures) Experiments: 1.  Make quan>ta>ve measurements. (Take data) 2.  Compare with expecta>on. (Analyze data) 3.  Make a conclusion. (Present results) 26 Example: Accelera>on due to gravity Expecta>on (known value): g=9.796 m/s2 Measurement: g = ± 0.2 m/s2
Conclusion: (Does the measured value agree with the known value?) ? g = 9700 ± 200 ? g = 9.7 m/s2 ? agree
disagree g = 9.7 ± 0.2 m/s2
g = 9.70 ± 0.02 m/s2
27 When do I need to use this in PHYS1140? Standard format 1.  value 2.  uncertainty 3.  units (significant figures) 1.  Take data (in your lab notebook) 2.  Analyze data (in your Mathema>ca calcula>ons) 3.  Present results (in your lab report discussion and conclusions) 28 Next: Significant figures how many digits to include in your result (like spelling, not following conven>on usually just makes you look ignorant, but some>mes it can cause real confusion) length = 10 ± 3 cm length = 5.32 ± 0.01 cm 29