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Accuracy, Precision ppt

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 Accuracy & Precision Two important points in measurement
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7/28/2019 Accuracy, Precision ppt

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Accuracy & Precision

Two important points in measurement

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Accuracy and Precision

Objective:

Explain the difference between the accuracyand precision.

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Definitions

Accuracy and Precision

…sounds like the samething…

…is there adifference??

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Accuracy = how close a measured value is to the actual (true)value .

For example, we would expect a balance to read 100 grams if weplaced a standard 100 g weight on it. If it doesn’t, then the

balance is inaccurate.

Accura

cy

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Precision

Precision = how close themeasured values are to each

other .

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A precise instrument also gives a consistent reading when it is used repeatedly for thesame measurements.

A

B

A beaker is weighed on A, 3 times:

The readings are: 73 g, 77 g, 71 g

It is then weighed on B, 3 times:The readings are: 75 g, 73 g, 74 g

Balance B has better precision .Its readings are grouped closer together .

E.g.

Precision = how close a measurement is toother measurements of the same thing.

Which scale is more precise?

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Threetargets withthree

arrows eachto shoot.

Can you hit the bull's-eye?

Bothaccurateandprecise

Precisebut notaccurate

Notaccurateor precise

How dothey

compare?

Can you define accuracy vs. precision?

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Determining accuracy and precision

Time Scale 1 Scale 2 Scale 3

8 a.m. 110 pounds 124 pounds 142 pounds

Noon 113 pounds 126 pounds 103 pounds

4 p.m. 109 pounds 125 pounds 115 pounds

8 p.m. 110 pounds 126 pounds 129 pounds

Weight of person who weighs about 125 pounds

PRECISE, BUTNOT ACCURATE

ACCURATE ANDPRECISE

NOT ACCURATENOT PRECISE

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Learning Check: Accuracy

Who is more accurate when measuring a bookthat has a true length of 17.0 cm? ( Accuracy = how

close a measurement is to the correct or accepted value. )Susan :17.0 cm, 16.0 cm, 18.0 cm, 15.0 cm

Amy :15.5 cm, 15.0 cm, 15.2 cm, 15.3 cm

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Learning Check: Precision

Who is more precise when measuring the same17.0 cm book?

Susan :17.0 cm, 16.0 cm, 18.0 cm, 15.0 cm

Amy :15.5 cm, 15.0 cm, 15.2 cm, 15.3 cm

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LearningCheck: Precision

Precision = how close a measurement is to other measurements of the same thing .

Which set is more precise?18.2 , 18.4 , 18.35 - SET 117.9 , 18.3 , 18.85 - SET 2

16.8 , 17.2 , 19.44 - SET 3

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Accuracy vs. Precision

High AccuracyHigh Precision

High PrecisionLow Accuracy

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Graduated Cylinder – Meniscus andParallax

Beware of Paral lax – the apparent shift in position when viewed at a differentangle.

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Learning Check

Which set of measurements of a 2.00-gstandard weight is the most precise?

• A. 2.00 g, 2.01 g, 1.98 g• B. 2.10 g, 2.00 g, 2.20 g• C. 2.02 g, 2.03 g, 2.04 g• D. 1.50 g, 2.00 g, 2.50 g

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Exit Quiz: Evaluate whether thefollowing are precise, accurate or both.

A c c u r a t e

N o t P r e c i s e

N o t A c c u r a te

P r e c i s e

A c c u r a t e

P r e c i s e

A B C


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