Measurements and Their Errors

Question 1

What are the SI Units

Answer 1

• Mass (kg)
• Length (m)
• Time (s)
  Amount of substance (mol)
  Temperature (K)
• Electric current (A)

Question 2

What are the Unit Prexfixes you need to know

Answer 2

Question 3

How do you convert between Electron Volts and Joules

Answer 3

1eV = 1.6x 10^-19 J

Question 4

What is Random Error

Answer 4

• Measurments vary due to unpredictable circumstance
• They cannot be corrected and can only be minimised by making more measurements and calculating a mean

Question 5

How do you reduce Random Error

Answer 5

• Take at least 3 random repeats and calculate a mean (shows anomalies)
• Use computers/cameras to reduce human error and increase precision
• Use appropriate equipment (micrometers rather than ruler)

Question 6

What is Systematic Error

Answer 6

• Measurements differ from the true value by a consistent amount each time
• Can be corrected by using a different technqiue

Question 7

How do you reduce Systematic Error

Answer 7

• Calibrate the equipment by measuring a known value
• In radiation experiments correct for background radiation by measuing it beforehand
• Look at readings at eye level to reduce parallax error

Question 8

What is Precision and Accuracy

Answer 8

• Precision - how close measurments are to each other and the mean
• Accuracy - how close a measurment is to the true value

Question 9

What does Repeatable, Reproducible and Resolution mean

Answer 9

Repeatable - when the original experimenter repeats the investigation using the same method and equipment and gets the same results

Reproducible - when somebody else using different equipment repeats the investigation and gets the same results

Resolution - the smallest change in a quantity being measured

Question 10

What is the Uncertainty in a Reading and in a Measurement

Answer 10

• The uncertainty in a reading (when one value is found) is ± half the resolution
• The uncertainty in a measurement (when the difference between two readings is found) is ± 1 resolution

Question 11

How is Uncertainty showed for Repeated Data

Answer 11

mean ± range/2

Question 12

How do you combine Uncertainties

Answer 12

• Adding/ subtracting data - Add Absolute Uncertainities
• Multiplying/ dividing data - Add Percentage Uncertainities
• When raising data with an uncertainity to a power - Multiply the Percentage Uncertainty by the Power
• When multiplying data with an uncertainty by a constant - multiply the absolute uncertainty by the constant but not the percentage uncertainty

Question 13

How do you find Percentage Uncertainties using Graphs

Answer 13

• Draw a steepest and shallowest line of worst fit that goes through all of the error bars
• Calculate the gradient of the lines
• The uncertainty is the difference between the best and worst gradients

Percentage Uncertainty = Best Gradient - Worst Gradient / Best Gradient x 100