Measurements and Their Errors Flashcards
What are the SI Units
- Mass (kg)
- Length (m)
- Time (s)
Amount of substance (mol)
Temperature (K) - Electric current (A)
What are the Unit Prexfixes you need to know
How do you convert between Electron Volts and Joules
1eV = 1.6x 10^-19 J
What is Random Error
- Measurments vary due to unpredictable circumstance
- They cannot be corrected and can only be minimised by making more measurements and calculating a mean
How do you reduce Random Error
- 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)
What is Systematic Error
- Measurements differ from the true value by a consistent amount each time
- Can be corrected by using a different technqiue
How do you reduce Systematic Error
- 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
What is Precision and Accuracy
- Precision - how close measurments are to each other and the mean
- Accuracy - how close a measurment is to the true value
What does Repeatable, Reproducible and Resolution mean
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
What is the Uncertainty in a Reading and in a Measurement
- 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
How is Uncertainty showed for Repeated Data
mean ± range/2
How do you combine Uncertainties
- 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
How do you find Percentage Uncertainties using Graphs
- 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