reliability in measurements. measurements must be accurate & precise
TRANSCRIPT
![Page 1: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/1.jpg)
Reliability in Measurements
![Page 2: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/2.jpg)
Measurements must beAccurate & Precise.
![Page 3: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/3.jpg)
•Accuracy is how close a measurement is to an accepted value (the book value)
•In other words, “did you get close to the correct measurement?”?”
![Page 4: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/4.jpg)
Example:
•Water boils at 100C. You boil water and measure the boiling point to be 98C. Is your measurement accurate? Accurate would have to have < 5% error.
•Yes, Although this value is close there is a small amount of error.
![Page 5: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/5.jpg)
•You boil the water a second time. This time, you find the water to boil at 76C. Are you accurate?
•NONO!! You didn’t get anywhere close to the accepted BP of water (100C)
Example:
![Page 6: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/6.jpg)
•How can you tell how accurate your measurements are?
•How much error do you have?
![Page 7: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/7.jpg)
•Percent Error = a calculation to determine how accurate you are
•It shows how much error you have
![Page 8: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/8.jpg)
•accepted value: the value you want to get; the “book value”
•experimental value: the value YOU get in an experiment
![Page 9: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/9.jpg)
•What do these weird lines mean in this formula?
The lines are absolute value marks which means you CANNOT get a negative answer!
![Page 10: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/10.jpg)
What are two reasons you might not make an
accurate measurement?
1. Human error 2. Machine error
![Page 11: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/11.jpg)
Let’s Practice!
1. The accepted boiling point for a sample of astatine 350C. A chemist boils a sample and finds the temperature to be 365C.
– What is her percent error? – Is she accurate?
![Page 12: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/12.jpg)
2. A student finds the mass of an object to be 19.5g. The accepted mass of the object is 12.2g. – What is his percent error? – Is he accurate?
![Page 13: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/13.jpg)
•Precision is how close a series of measurements are to one another.
![Page 14: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/14.jpg)
Example:
•A student boils water 4 times and gets the following data:
Trial 1: 65C Trial 3: 67CTrial 2: 65C Trial 4: 66C
•Is the student accurate?•NO! The BP of water is 100C
![Page 15: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/15.jpg)
Trial 1: 65C Trial 3: 67CTrial 2: 65C Trial 4: 66C
•Is the student precise?
•YES! because all the BP’s were close to the same value.
•Precision has NOTHING to do with the accepted value!
![Page 16: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/16.jpg)
Stop for a moment . . .
![Page 17: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/17.jpg)
•Precision can be determined by the equipment used to make the measurement
![Page 18: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/18.jpg)
AND getting the same measurement over and
over with a small amount of error
each time – that’s precision!
![Page 19: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/19.jpg)
•Which reading is more precise? 8.50 g or 8.503 g
•8.503 g is more precise because it has more “numbers”
•These numbers are called significant figures
![Page 20: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/20.jpg)
•sig. figs. represent precision
•sig. figs. include all known numbers plus one estimated number (not known for sure)
•example: In the number 8.503, the digits known for sure are 8, 5, and 0, but “3” is the estimated number
![Page 21: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/21.jpg)
•IMPORTANT: If the equipment you are using is DIGITAL, the estimated digit has been done for you!!!
•IMPORTANT: If the equipment is NOT digital, YOU have to estimate one place past the number you know for sure!
![Page 22: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/22.jpg)
To find the “scale” of a piece of equipment
Try:.1 .2.512
![Page 23: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/23.jpg)
*Find the “uncertainty” in the measurement:
1st: What is the scale here?
the scale is 1C
2nd: Read instrument 87C for sure
3rd: Go one place PAST what we know and “estimate”
87.5C
![Page 24: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/24.jpg)
*Find the “uncertainty” in the measurement:
1st: What is the scale here?
the scale is 1C
2nd: Read instrument 35C for sure
3rd: Go one place PAST what we know and “estimate”
35.0C
![Page 25: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/25.jpg)
*Find the “uncertainty” in the measurement:
1st: What is the scale here?
the scale is .2mL
2nd: Read instrument 6.6mL for sure
3rd: Go one place PAST what we know and “estimate”
6.60mL
![Page 26: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/26.jpg)
*Find the “uncertainty” in the measurement:
1st: What is the scale here?
the scale is .5mL
2nd: Read instrument 11.5mL for sure
3rd: Go one place PAST what we know and “estimate”
11.50ml
1st: What is the scale here?
the scale is .5mL
2nd: Read instrument 11.5mL for sure
3rd: Go one place PAST what we know and “estimate”
11.50ml
![Page 27: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/27.jpg)
*Find the “uncertainty” in the measurement:
1st: What is the scale here? the scale is .1cm
2nd: Read instrument 5.1cm for sure
3rd: Go one place PAST what we know and “estimate”
5.15cm
![Page 28: Reliability in Measurements. Measurements must be Accurate & Precise](https://reader038.vdocuments.mx/reader038/viewer/2022102805/55143d21550346284e8b475a/html5/thumbnails/28.jpg)
Let’s practice . . .