Measurements & Uncertainties (OCR A Level Physics): Flashcards
Exam code: H556
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What is meant by the precision of measurements?
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Cards in this collection (24)
What is meant by the precision of measurements?
Precision refers to how close measured values are to each other, resulting in little spread about the mean value.
What is meant by the accuracy of measurements?
Accuracy is how close the measurements are to the true value.
What is meant by a random error?
A random error is an unpredictable fluctuation in an instrument's readings caused by uncontrollable factors, which affects the precision of measurements.
What is meant by a systematic error?
A systematic error is a consistent error arising from a faulty instrument or a flaw in the experimental method, which affects the accuracy of all readings.
How can random errors be reduced?
By repeating measurements several times and calculating an average.
True or False?
Systematic errors can be reduced by repeating measurements and calculating a mean.
False.
Repeating measurements only reduces random error. Systematic errors are consistent every time the instrument or method is used, so they must be reduced by recalibrating instruments or correcting the technique.
A zero error is a type of .......... error that occurs when an instrument gives a reading when the true value is zero.
A zero error is a type of systematic error that occurs when an instrument gives a reading when the true value is zero.
How is a zero error corrected?
By subtracting the offset value from each measurement taken.
Define uncertainty.
Uncertainty is the range of values around a measurement within which the true value is expected to lie; it is an estimate.
What is the difference between an error and an uncertainty?
An error is caused by equipment or methodology and makes a reading differ from the true value. An uncertainty is an estimated range around a measurement within which the true value is expected to lie.
What is the uncertainty in a single reading taken from a scale?
± half the smallest division on the scale.
How is the uncertainty in repeated data calculated?
Half the range: ± ½ × (largest value − smallest value).
The uncertainty in a .......... reading is ± the last significant digit, unless otherwise quoted.
The uncertainty in a digital reading is ± the last significant digit, unless otherwise quoted.
When adding or subtracting measurements, how are their uncertainties combined?
Their absolute uncertainties are added together.
When multiplying or dividing measurements, or raising a measurement to a power, how are the uncertainties combined?
For multiplying or dividing, add the percentage (or fractional) uncertainties. For a value raised to a power, multiply the percentage uncertainty by the power.
True or False?
The uncertainty in a constant such as π is taken to be zero.
True.
Constants have no associated measurement uncertainty, so it is taken as zero.
What is an error bar?
An error bar drawn on a graph shows the absolute uncertainty in a plotted value, either vertically (for y-values) or horizontally (for x-values).
What is the difference between the line of best fit and the line of worst fit?
The line of best fit passes as close as possible to all the points. The line of worst fit is the steepest or shallowest line that still fits within all the error bars.
How is the percentage uncertainty in a gradient determined from a graph?
By comparing the gradients of the best fit and worst fit lines drawn through the error bars.
How is the percentage uncertainty in the y-intercept found from a graph?
By comparing the y-intercepts of the best fit and worst fit lines.
What is percentage difference?
The percentage difference compares the experimental (measured) value obtained in an experiment to the accepted (true) value.
The smaller the percentage difference, the more .......... the results of an experiment.
The smaller the percentage difference, the more accurate the results of an experiment.
True or False?
Percentage difference is a type of percentage uncertainty.
False.
Percentage difference compares an experimental value with an accepted value; it is a measure of accuracy, not an uncertainty.
Where can the accepted value of a quantity be found for calculating percentage difference?
From a value labelled on a component (e.g. a resistor or capacitor) or from a databook.
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