Download presentation

1
**Reliability in Measurements**

2
Measurements must be Accurate & Precise.

3
**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?”?”

4
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.

5
Example: You boil the water a second time. This time, you find the water to boil at 76C. Are you accurate? NO! You didn’t get anywhere close to the accepted BP of water (100C)

6
**How can you tell how accurate your measurements are?**

How much error do you have?

7
**Percent Error = a calculation to determine how accurate you are**

It shows how much error you have

8
**accepted value: the value you want to get; the “book value”**

experimental value: the value YOU get in an experiment

9
**What do these weird lines mean in this formula?**

The lines are absolute value marks which means you CANNOT get a negative answer!

10
**What are two reasons you**

might not make an accurate measurement? Human error Machine error

11
Let’s Practice! 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?

12
**A student finds the mass of an object to be 19. 5g**

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?

13
**Precision is how close a series of measurements are to one another.**

14
**Example: A student boils water 4 times and gets the following data:**

Trial 1: 65C Trial 3: 67C Trial 2: 65C Trial 4: 66C Is the student accurate? NO! The BP of water is 100C

15
**Trial 1: 65C Trial 3: 67C Trial 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!

16
Stop for a moment . . .

17
**Precision can be determined by the equipment used to make the measurement**

18
**AND getting the same measurement over and**

over with a small amount of error each time – that’s precision!

19
**8.503 g is more precise because it has more “numbers”**

Which reading is more precise? 8.50 g or g 8.503 g is more precise because it has more “numbers” These numbers are called significant figures

20
**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

21
**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!

22
**To find the “scale” of a piece of equipment**

Try:

23
***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

24
***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

25
***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

26
***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

27
***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

28
Let’s practice . . .

Similar presentations

Presentation is loading. Please wait....

OK

CH. 2 - MEASUREMENT Units of Measurement.

CH. 2 - MEASUREMENT Units of Measurement.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on hard gelatin capsule solubility Ppt on profit planning in banks Ppt on bluetooth communication standard Presentations ppt online maker Ppt on minimum wages act mumbai Funny ppt on marriage Ppt on market friendly staten Download ppt on quadrilaterals and their properties Ppt on waves tides and ocean currents activity Ppt on big data analytics