Measurements and Uncertainties

Question 1

What does accurate/accuracy mean?

Answer 1

An experiment is accurate if the quantity being measured has a value that’s very close to the commonly accepted or true value.

Question 2

What does precision mean?

Answer 2

The results of an experiment are precise if they are close together and have a small range. The smaller the range the higher the precision.

Question 3

What is a Systematic Error?

Answer 3

An error that does not happen by chance but instead is introduced by an inaccuracy in the apparatus or its use by the person conducting the investigation.

Question 4

What is a Zero Error?

Answer 4

An error that occurs when the apparatus shows a non-zero value when it should be a value of exactly zero.

Question 5

What is a Parallax Error?

Answer 5

An error produced whenever a scale, gauge, or pointer is observed wrongly during an experiment due to the position of viewing and perception.

Question 6

What is a Random Error?

Answer 6

A random error is an experimental error caused by unknown or unpredictable changes to the apparatus or conditions.

Question 7

How do you reduce random errors?

Answer 7

Can be reduced or totally eliminated by the use of better techniques and instruments. This increases the accuracy of the experiment.

Question 8

How do you reduce systematic errors?

Answer 8

Same as random errors.

Question 9

What does resolution mean?

Answer 9

The smallest change in quantity that an instrument can measure. The higher the resolution, the higher the precision in repeat readings.

Question 10

What is the absolute uncertainty/error?

Answer 10

The size of the range of values in which the true value of the measurement probably lies.

Question 11

How do you find percentage uncertainty?

Answer 11

(uncertainty/average value ) * 100

Question 12

How do you find the uncertainty for multiple readings?

Answer 12

range of readings / 2

Question 13

What are the rules for determining percentage uncertainty?

Answer 13

• If y = a * b then % uncertainty of y = % uncertainty of a + % uncertainty of b
• If y = a / b then % uncertainty of y = % uncertainty of a + % uncertainty of b
• If y = a^n then % uncertainty of y = n * % uncertainty of a

Question 14

How do you determine uncertainty in the gradient?

Answer 14

1. Errors bars may be added to each plotted point if the data points are not too scattered
2. Draw line of best fit through scattered points (or error bars). Draw worst acceptable line.
3. Determine the gradient of best fit line and gradient of worst acceptable line.
4. Uncertainty = | gradient of best fit line - gradient of worst acceptable line |
5. Percentage uncertainty in the gradient can be determined using (uncertainty/gradient of best fit line) * 100

Question 15

How do you determine uncertainty in the y-intercept using maximum and minimum gradients?

Answer 15

1. Errors bars may be added to each plotted point if hte data points are not too scattered
2. Draw a best fit line through the scattered points (or error bars). The worst acceptable line is then drawn.
3. Determine y-intercept of both lines.
4. Uncertainty = | y-intercept of best fit line - y-intercept of worst acceptable line |
5. Percentage uncertainty in the y-intercept = (uncertainty/y-intercept) * 100

Question 16

How do you calculate % difference?

Answer 16

((experimented value - accepted value) / accepted value ) * 100