Physical Quantities and Units (And Uncertainties) Flashcards
What are the 7 base quantities and their units?
Length ~ m
Mass ~ kg
Time ~ s
Temperature ~ K
Amount of Substance ~ mol
Light intensity ~ Cd
Electric current ~ A
Giga
10 power 9
Mega
10 power 6
Tera
10 power 12
Pico
10 power -12
Nano
10 power -9
Milli
10 power -3
Micro
10 power -6
Deci
10 power -1
Centi
10 power -2
Kilo
10 power 3
Physical quantity
Any quantity that can be measured
Base Quantity
A quantity that cannot be further split up into simpler quantities.
Derived Quantity
A derived quantity is formed due to some manipulation of the base quantities.
eg: speed, acceleration etc
Precision
Precision measures how close two or more values are to each other (closeness). If a measurement is repeated several times, then they can be described as precise if all the values are similar to each other.
Accuracy
How close the measured value is to the actual or true value.
Random Error
🔹Random errors are due to unpredictable fluctuations in an instrument’s readings as a result of different factors such as an error caused by the experimenter (eg: parallax error) or by environmental conditions.
🔹This affects the precision of the measurements taken, causing a wider spread of results about the mean value.
🔹To reduce random error: repeat measurements several times and calculate an average from them.
🔹Affects precision.
Systematic Error
🔹Systemic errors arise (due to the system) from the use of faulty instruments being used or from flaws in the experimental method.
🔹This type of error is repeated every time the instrument is used or the method is followed which affects the accuracy of all readings obtained.
🔹To reduce systemic errors; the instrument being used should be recalibrated or the technique being used should be readjusted or corrected.
🔹Affects accuracy.
How can we reduce Systematic Errors?
Instruments should be recalibrated or the technique being used should be corrected or adjusted.
What is a Zero Error?
🔹This is a type of systematic error which occurs when an instrument gives a reading when the true reading is zero.
🔹This introduces a fixed error into the readings which must be accounted for when the results are recorded.
What is an uncertainty?
The uncertainty is an estimate of the difference between the measured reading and the true value.
Are uncertainties and errors the same?
Uncertainties are not the same as errors
• Errors can be thought of as issues with equipment or methodology that cause a reading to be different from the true value
• The uncertainty is a range of values around a measurement within which the true value is expected to lie, and is an estimate
