Measurments And Errors Flashcards
What is 1eV in J
1eV = 1.6×10^-19 J
What is a random error?
An error that affects precision and cannot be completely removed, it causes differences in measurements.
What is systematic error?
An error that affects accuracy and occurs due to faults in equipment or experimental method, causing the result to be too large/small by the same amount each time.
What are three ways to reduce random error?
Take a multiple results and calculate the mean.
Use a computer or data logger.
Use higher resolution equipment.
What is a parallax error?
Reading the scale at a different angle each time. To correct this, read the scale at eye level to reduce parallax error.
How can systematic error be reduced?
Calibrate apparatus before using it e.g. zero the balance when it is empty.
Why should you measure the background radiation before measuring the radioactivity of a source?
So that only the source’s radioactivity is measure, by accounting for background radiation systematic error is reduced.
What is repeatability?
If the original experimenter can redo the experiment with the same equipment and method then get the same results, it is repeatable.
What is reproducibility?
If the experiment is redone by a different person or with different techniques and equipment and the same results re found, it is reproducible.
What is meant by resolution?
The smallest change in the quantity being measured that gives a recognisable change in reading.
What is absolute uncertainty?
Uncertainty given as a fixed quantity e.g. 7 +/- 0.6 V
What is the percentage uncertainty in 17 +/- 3A?
3/17 * 100 = 17.647%
= 18%
How can percentage and fractional uncertainty be reduced?
Measure larger quantities e.g. a longer rope will have a smaller percentage uncertainty than a shorter one.
The time for 10 swings of a pendulum is 13 +/- 0.3s, what is the time and uncertainty for 1 swing?
1 swing = 13/10 = 1.3s
uncertainty = 0.3/10 = 0.03s
Time = 1.3 +/- 0.03s
What is the difference between a reading and a measurement?
Reading are when value is found, measurements are when the difference between 2 readings is found.
How to find the absolute uncertainty of multiple value
Half the range and get rid of outliers
what do you do with uncertainty when multiplying/dividing data?
You will convert them to percentage uncertainties and then add them together.
When drawing a line of best fit on a graph with error bars what must you do?
Make sure the line of best fit goes through all the error bars.
How do you find the uncertainty in the gradient of a line of best fit?
Draw the steepest or shallowest line of worst fit, it must go through all the error bars.
Calculate the gradient of the best and the worst line, the uncertainty is the difference between the best and worst gradients.
What do we do with the uncertainties when we are multiplying or dividing?
We multiply/divide the uncertainties by the same constant
