quantities and measurement Flashcards
(21 cards)
what are the 7 base units?
kg, m, s, A, K, mol, cd
what are derived units?
a unit expressed as a product and/or quotient of the 7 base units
what are homogenous equations?
an equation is homogenous if every term on both sides of the equation have the same SI base units
what is the order of magnitude and their prefixes?
tera (T) - x10ˆ12
giga (G) - x10ˆ9
mega (M) - x10ˆ6
kilo (k) - x10ˆ3
deci (d) - x10ˆ-1
centi (c) - x10ˆ-2
mili (m) - x10ˆ-3
micro (u) - x10ˆ-6
nano (n) - x10ˆ-9
pico (p) - x10ˆ-12
what are the 3 steps to make an estimate of physical quantities?
1) express the more complicated quantity in terms of other simpler quantities using a formula first (find a way to calculate the estimate)
2) compare with known values in daily life
3) give the figure to 1 sf (an estimate is not very precise)
what is the definition of random error?
(2 points)
random error is an error that causes measurements to be sometimes larger than the true value and sometimes smaller than the true value
they are equally likely to be positive or negative with respect to the true value
what are 2 ways to reduce random error?
1) repeat measurements to obtain an average
2) plotting a graph to obtain line/curve of best fit
what are 2 examples of random error?
1) random variations in external experimental conditions
2) human error (parallax error, inability of an experimenter to repeat his actions precisely)
what is systematic error? (3 points)
systematic error is an error which causes measurements to be either, always larger than the true value, or always smaller than the true value
they are of the same magnitude with the same sign
they are eliminated, not reduced
what are 3 examples of systematic errors?
1) zero error of an instrument
2) incorrectly calibrated instrument
3) incorrect experimental procedure
what is precision and what is it caused by?
precision refers to the degree of agreement (ie scatter, spread) of repeated measurements of the same quantity (distance from mean)
small random error = high precision
what is accuracy and what is it caused by?
accuracy refers to the degree of agreement between the result of measurement(s) and the true value of the quantity (distance from true value)
small systematic error = high accuracy
what is the acronym to connect errors with precision and accuracy?
SA RP
how to determine absolute uncertainty of a scale reading?
normally estimated to be half the smallest division of the scale of the instrument
how to determine absolute uncertainty of a measurement (requires 2 readings)
absolute uncertainty is 2 x half the smallest division (just the smallest division)
what is rule 1 (for add/subtract) for calculating uncertainty?
Y = 2A - 3B
dY = 2dA + 3dB
retain coefficients
uncertainties are always added
what is rule 2 (for multiply/divide/power) for calculating uncertainty?
Y = 6Xˆ2 x Zˆ3
dY/Y = 2(dX/X) + 3(dZ/Z)
coefficients ignored as they are considered error-free
bring down power, uncertainties are always added
what is rule 3 for calculating uncertainty?
dY = 1/2(Ymax - Ymin)
what is a scalar quantity and what are examples of scalar quantities?
a scalar quantity are physical quantities that have magnitude only (can be +/-)
examples are mass, distance, speed, time, temperature, work done, pressure etc
what is a vector quantity and what are its examples?
vectors are physical quantities that have both magnitude and direction
examples are displacement, velocity, acceleration, force, moment etc
what are the rules for the components method for addition of vectors?
1) components must be perpendicular to each other
2) components cannot be bigger than the original vector
3) original vector must be the hypotenuse of the right-angled triangle
