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The Real World

“Life, unlike a math textbook, doesn’t have all of the answers in the back of the book.” Source lost. The Real World. Technicians get paid a reasonable salary to follow recipes. Scientists get paid higher salaries to write recipes for technicians to follow.

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The Real World

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  1. “Life, unlike a math textbook, doesn’t have all of the answers in the back of the book.”Source lost

  2. The Real World • Technicians get paid a reasonable salary to follow recipes. • Scientists get paid higher salaries to write recipes for technicians to follow.

  3. Good Time to Review Definitions of Precision and Accuracy • Precision • Random errors are small • Give examples of random errors • Results are extremely reproducible • Large number of significant digits can be justified • Experimenter is skilled • Accuracy • Systematic errors are small • Give examples of systematic errors • Result reveals truth

  4. Experiments with large random errors • Social sciences • Political polling • Economics • Opinion polls • Astronomical measurements • Cosmic Ray research! • The value of the Hubble constant • Experiments with large systematic errors • Poorly calibrated equipment • Consistent parallax • Voltmeter with low input impedance or inaccurate components • Basically indefensible

  5. A Digression on Error Analysis and Significant Digits • The number of “significant digits” that you report in lab reports will be taken very seriously • This is “where the rubber hits the road” • If too small, your work will not be taken seriously • You get no credit for claiming to have measured the speed of light to be 3x1010 cm/sec in 2009! • If too large, your work is indefensible and effectively fraudulent. (You are claiming something you have, in fact, not done.)

  6. How Do You Determine How May Digits Are Really Justified? • Hg manometer? • What are the sources of systematic error? • How could you “calibrate” your measurements? • How precisely (or is it accurately?) can you read the mercury levels? • Other gauges • How do you calibrate them? • How precisely (or is it accurately?) can you read them?

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