Questions:
1. Do all the physical constants have units?
Yes or No. Four students have been picked to answer the question.
Questions:
1. Do all the physical constants have units?
Yes or No
Dimensionless fundamental physical constants include:
α, the fine structure constant, the coupling constant for the electromagnetic interaction
(≈ 1⁄137). ...
Bohr’s model of the atom
μ or β, the proton-to-electron mass ratio, the rest mass of the proton divided by that of
the electron (≈1836). ... Why not neutron-to-electron mass ratio?
αs, the coupling constant for the strong force (≈1)
Etc.
Questions:
1. Do all the physical constants have units?
2. Is it ever possible for the uncertainty in a physical quantity to be zero? Or can a
physical quantity be defined without an error?
Yes or No. Four students have been picked to answer the question.
Questions:
1. Do all the physical constants have units?
2. Is it ever possible for the uncertainty in a physical quantity to be zero? Or can a
physical quantity be defined without an error?
Yes or No
Electric constant
Magnetic constant,
By definition!
Speed of light, c.
Questions:
1. Do all the physical constants have units?
2. Is it ever possible for the uncertainty in a physical quantity to be zero? Or can a
physical quantity be defined without an error?
Yes or No
Electric constant
Magnetic constant,
By definition!
Speed of light, c.
Any relation between c and o and o?
Define length (meter) and time (second), precise measurements yield c.
Speed of Light
Historically, we defined both meter (by a meter-stick) and second, then
measure the speed of light.
1) What is the most likely factor which will change the length of a meter-stick?
Any suggestions?
2) How precise can one measure its length now?
(100m, 10m, 1 m, 0.1m, 0.01m)
Close your eyes and let us take a poll.
Speed of Light
Historically, we defined both meter (by a meter stick) and second, then
measure the speed of light. What is the most likely factor which will
change the length of a meter-stick? How precise can one measure its
length now?
General Conference on Weights and Measures (CGPM)
Order a stainless steal rod with length 1 centimeter in the CSE shop, what is the
smallest uncertainty that you can specify without a rejection from the mechanist?
Speed of Light
Historically, we defined both meter (by a meter stick) and second, then
measure the speed of light. What is the most likely factor which will
change the length of a meter-stick? How precise can one measure its
length now?
General Conference on Weights and Measures (CGPM)
Order a stainless steal rod with length 1 centimeter in the CSE shop, what is the
smallest uncertainty that you can specify without a rejection from the mechanist?
Do you know the diameter of your hair?
Speed of Light
Length: platinum-iridium bar; Time:?
In the laboratory, among the following physical quantities: weight, length,
current, frequency, which one we can measure with the highest accuracy?
Discuss with your classmates briefly.
Three students have been picked to answer this question.
Speed of Light
Length: platinum-iridium bar; Time:?
In the laboratory, among the following physical quantities: weight, length,
current, frequency, which one we can measure with the highest accuracy?
Cesium clock: the duration of 9,192,631,770 periods (ten significant
figures) of the radiation corresponding to the transition between the two
hyperfine levels of the ground state of the cesium 133 atom at rest.
Speed of Light
Previously, we defined both meter (by a meter stick) and second, then
measure the speed of light. What is the most likely factor which will
change the length of a meter-stick? How precise can one measure its
length now?
Cesium clock: the duration of 9,192,631,770 periods (ten significant
figures) of the radiation corresponding to the transition between the two
hyperfine levels of the ground state of the cesium 133 atom at rest.
Atomic clock (frequency) defines time (ten significant figures) along with
c = 2.99792458 x 108 m/s. (nine significant figures, defined)
This allows us to define the meter.
Accuracy: how many significant figures in the definition of meter?
Two students have been picked to answer this question.
Questions:
2. Is it ever possible for the uncertainty in a physical quantity to be zero? Yes or No
question
Now both 0 and c are defined, what will happen to 0?
Thus most of physical quantities have uncertainties.
Some Fundamental Constants of Physics
2008 Edition
An interesting answer appeared in “Quora”
What is the difference between 2 and 2.0?
I sincerely hope from now on your answer will never given in this way.
A linear function
The linear function w = a*u + b is a very general one for many different situations,
let us consider the simplest one first, w = y, and u = x.
Fitting data to a straight line
There are two way to represent the same straight line:
Can you give any guideline to choose y(x) or x(y)?
1.
Thermal expansion coefficient (length vs. temperature)
of an Al rod.
2. Non-linear Kerr rotation(q) vs. temperature(T): Sr2IrO4
(a previously cited example)
In these two cases, which physical parameter(s) we have a
better control?
Fitting data to a straight line
There are two way to represent the same straight line:
Can you give any guideline to choose y(x) or x(y)?
For the given experimental measurement, usually x is the variable that we
have a better control with a smaller error and y is the physical property
that is measured and tends to have a larger error. We always try our best
to estimate the errors on both x-values and y-values.
Fitting data to a straight line
Thus for a linear equation:
The deviation di between each of the measured
values yi and the corresponding calculated values.
Commonly, the deviation (si) of each yi -value is different.
chi-squared of the data: sum of weighted deviations
The best fitting means minimizing
with respect to some variables?
Can you tell us what are the variables?