Planck_constant

context: First recognized in 1900 by Max Planck, it was originally the proportionality constant between the minimal increment of energy, E, of a hypothetical electrically charged oscillator in a cavity that contained black body radiation, and the frequency, f, of its associated electromagnetic wave. In 1905 the value E, the minimal energy increment of a hypothetical oscillator, was theoretically associated by Einstein with a "quantum" or minimal element of the energy of the electromagnetic wave itself. The light quantum behaved in some respects as an electrically neutral particle, as opposed to an electromagnetic wave. It was eventually called the photon.
qas: answers: text: value E
question: What is considered the minimal energy increment of a hypothetical oscillator?

answers: text: 1905
question: In what year was the value E associated by Einstein with quantum theories of energy?

answers: text: Einstein
question: Who discovered an association between the value E and quantum energy?

answers: text: neutral particle
question: What did the light quantum behave the same as in laboratory experiments?

answers: text: neutral
question: What type of charge did a particle have that behaved similarly to light quantum energy?

answers: text: E
question: What is energy abbreviated to in science?

answers: text: f
question: What is frequency also known as in science?

answers: text: quantum
question: What term describes a small amount of element?

answers: text: an electrically neutral particle
question: What did the light quantum, in some ways, behave as?

answers: text: The light quantum
question: What was later termed the photon?

answers: text: 1900
question: When did Max Planck first recognize the value of the Planck constant?

answers: text: Einstein
question: Which scientist associated the Planck constant with a quantum five years after Planck's recognition?

answers: text: an electrically neutral particle
question: Instead of an electromagnetic wave, what did the light quantum behave as in some regards?

answers: text: the photon
question: What is the simple name given to the light quantum today?

context: Classical statistical mechanics requires the existence of h (but does not define its value). Eventually, following upon Planck's discovery, it was recognized that physical action cannot take on an arbitrary value. Instead, it must be some multiple of a very small quantity, the "quantum of action", now called the Planck constant. Classical physics cannot explain this fact. In many cases, such as for monochromatic light or for atoms, this quantum of action also implies that only certain energy levels are allowed, and values in between are forbidden.
qas: answers: text: h
question: What does classical statistics mechanics not define the value of?

answers: text: h
question: What is required to exist in classical statistics mechanics?

answers: text: physical action
question: After Planck's findings, what was determined could not take on an arbitrary value?

answers: text: the Planck constant
question: What is the "quantum of action" called?

answers: text: quantum of action
question: What does the Planck Constant refer to?

answers: text: h
question: Classical statistical mechanics requires the existence of what?

answers: text: that physical action cannot take on an arbitrary value
question: What was realized after Planck's discovery?

answers: text: quantum of action
question: What is the Planck constant formerly known as?

answers: text: that only certain energy levels are allowed
question: Regarding atoms, what does the Planck constant imply?

answers: text: forbidden
question: Regarding atoms, what are values in between certain energy levels considered by the Planck constant?

answers: text: physical action cannot take on an arbitrary value
question: Following Planck's discovery, what was realized about values of physical action?

answers: text: the "quantum of action"
question: The Planck constant initially was given what name?

answers: text: Classical physics cannot explain this fact
question: How is the proportional nature of the Planck constant explained?

answers: text: only certain energy levels are allowed, and values in between are forbidden.
question: For certain cases of light or atoms, what does the quantum of action yield?

context: Equivalently, the smallness of the Planck constant reflects the fact that everyday objects and systems are made of a large number of particles. For example, green light with a wavelength of 555 nanometres (the approximate wavelength to which human eyes are most sensitive) has a frequency of 7014540000000000000♠540 THz (7014540000000000000♠540×1012 Hz). Each photon has an energy E = hf = 6981358000000000000♠3.58×10−19 J. That is a very small amount of energy in terms of everyday experience, but everyday experience is not concerned with individual photons any more than with individual atoms or molecules. An amount of light compatible with everyday experience is the energy of one mole of photons; its energy can be computed by multiplying the photon energy by the Avogadro constant, NA ≈ 7023602200000000000♠6.022×1023 mol−1. The result is that green light of wavelength 555 nm has an energy of 7005216000000000000♠216 kJ/mol, a typical energy of everyday life.
qas: answers: text: particles
question: What are common things like furniture and stationary objects actually made of?

answers: text: 555 nanometres
question: Which light wavelength is the human eye most sensitive to?

answers: text: green
question: What color of light is the human eye most sensitive to?

answers: text: the fact that everyday objects and systems are made of a large number of particles
question: What does the smallness of the Planck constant show?

answers: text: 555 nanometres
question: At about what wavelength of light are human eyes most sensitive?

answers: text: 7014540000000000000♠540 THz
question: What frequency does green light with a wavelength of 555 nanmetres have?

answers: text: by multiplying the photon energy by the Avogadro constant
question: How is the energy from one mole of photos computed?

answers: text: 7005216000000000000♠216 kJ/mol
question: How much energy does a green light of wavelength 555 nm contain?

answers: text: 555 nanometres
question: What is the wavelength of light to which human eyes are most sensitive?

answers: text: 7014540000000000000♠540 THz
question: What is the frequency of the light to which the human eye is most sensitive?

answers: text: 6981358000000000000♠3.58×10−19 J
question: What is the energy of a photon?

answers: text: 7005216000000000000♠216 kJ/mol
question: How much energy is contained in the light to which human eyes are most sensitive?

context: In the last years of the nineteenth century, Planck was investigating the problem of black-body radiation first posed by Kirchhoff some forty years earlier. It is well known that hot objects glow, and that hotter objects glow brighter than cooler ones. The electromagnetic field obeys laws of motion similarly to a mass on a spring, and can come to thermal equilibrium with hot atoms. The hot object in equilibrium with light absorbs just as much light as it emits. If the object is black, meaning it absorbs all the light that hits it, then its thermal light emission is maximized.
qas: answers: text: black-body
question: What type of radiation was Planck studying in the late 19th century?

answers: text: forty
question: How many years prior to Planck's study had the scientific community first discussed black body radiation?

answers: text: Kirchhoff
question: What scientist first studied black body radiation?

answers: text: hot atoms
question: What is required for the electromagnetic field to come to thermal equilibrium?

answers: text: light
question: What does a hot object in equilibrium absorb as much as it emits?

answers: text: the problem of black-body radiation
question: What was Planck studying in the last part of the nineteenth century?

answers: text: Kirchhoff
question: Who posed the problem of black-body radiation?

answers: text: hotter
question: Cooler objects glow less than objects that are what?

answers: text: it absorbs all the light
question: What does a black object do to any of the light that hits it?

answers: text: thermal light emission
question: What is maximized as a result of a black object absorbing all the light that hits it?

answers: text: black-body radiation
question: Planck studied what problem posed originally by Kirchhoff?

answers: text: its thermal light emission is maximized.
question: If an object is black, what is known about its thermal light emission?

answers: text: absorbs just as much light as it emits
question: What is known about the light absorption of a hot object in equilibrium with light?

answers: text: laws of motion
question: Electromagnetic fields obey what laws?

context: The assumption that black-body radiation is thermal leads to an accurate prediction: the total amount of emitted energy goes up with the temperature according to a definite rule, the Stefan–Boltzmann law (1879–84). But it was also known that the colour of the light given off by a hot object changes with the temperature, so that "white hot" is hotter than "red hot". Nevertheless, Wilhelm Wien discovered the mathematical relationship between the peaks of the curves at different temperatures, by using the principle of adiabatic invariance. At each different temperature, the curve is moved over by Wien's displacement law (1893). Wien also proposed an approximation for the spectrum of the object, which was correct at high frequencies (short wavelength) but not at low frequencies (long wavelength). It still was not clear why the spectrum of a hot object had the form that it has (see diagram).
qas: answers: text: thermal
question: What do scientists assume black body radiation is?

answers: text: accurate
question: What kind of prediction does the assumption that black body radiation is thermal lead to?

answers: text: colour
question: What type of changes in the light a hot object emits as the object's temperature changes?

answers: text: Stefan–Boltzmann law
question: What law describes the changes in light emitted by a hot object?

answers: text: thermal
question: What assumption that black-body radiation is what leads to an accurate prediction?

answers: text: the total amount of emitted energy goes up with the temperature according to a definite rule
question: What does the Stefan-Boltzmann law state?

answers: text: the colour of the light
question: What about a hot object changes with the temperature?

answers: text: white hot
question: What color is hotter than "red hot"?

answers: text: the mathematical relationship between the peaks of the curves at different temperatures
question: What did Wilhelm Wien discover?

answers: text: the Stefan–Boltzmann law
question: What rule predicts that emitted energy increases with temperature?

answers: text: the colour of the light given off
question: What characteristic of the light emitted by a hot object changes with temperature?

answers: text: Wilhelm Wien
question: Who discovered the mathematical relationship between peaks and curves of light at different temperatures?

answers: text: Wien's displacement law
question: The rule that adjust the curve at different temperatures is known as what?

answers: text: at low frequencies (long wavelength)
question: Wien's spectrum model could not predict accurate at what end of the spectrum?

context: Prior to Planck's work, it had been assumed that the energy of a body could take on any value whatsoever – that it was a continuous variable. The Rayleigh–Jeans law makes close predictions for a narrow range of values at one limit of temperatures, but the results diverge more and more strongly as temperatures increase. To make Planck's law, which correctly predicts blackbody emissions, it was necessary to multiply the classical expression by a complex factor that involves h in both the numerator and the denominator. The influence of h in this complex factor would not disappear if it were set to zero or to any other value. Making an equation out of Planck's law that would reproduce the Rayleigh–Jeans law could not be done by changing the values of h, of the Boltzmann constant, or of any other constant or variable in the equation. In this case the picture given by classical physics is not duplicated by a range of results in the quantum picture.
qas: answers: text: any
question: Before Planck, it was assumed that the energy of a body could take on what value?

answers: text: a narrow range
question: The Rayleigh-Jeans law makes close predictions for what amount of values?

answers: text: blackbody emissions
question: What does Planck's law correctly predict?

answers: text: h
question: In making Planck's law, what was in both the numerator and denominator of the formula that was used?

answers: text: that the energy of a body could take on any value whatsoever
question: Planck's work disproved what assumption?

answers: text: The Rayleigh–Jeans
question: What rule predicted narrow range of energy values at lower temperatures?

answers: text: multiply the classical expression by a complex factor that involves h in both the numerator and the denominator
question: Planck's law involved what necessary mathematical step to correctly predict blackbody emission?

answers: text: Making an equation out of Planck's law that would reproduce the Rayleigh–Jeans law could not be done
question: Changing values of n, the Boltzmann constant, or other variables resulted in learning what about Planck's law?

answers: text: the picture given by classical physics is not duplicated by a range of results in the quantum picture
question: The disparity between Planck's law and the Rayleigh-Jeans law led to what conclusion?

context: The black-body problem was revisited in 1905, when Rayleigh and Jeans (on the one hand) and Einstein (on the other hand) independently proved that classical electromagnetism could never account for the observed spectrum. These proofs are commonly known as the "ultraviolet catastrophe", a name coined by Paul Ehrenfest in 1911. They contributed greatly (along with Einstein's work on the photoelectric effect) to convincing physicists that Planck's postulate of quantized energy levels was more than a mere mathematical formalism. The very first Solvay Conference in 1911 was devoted to "the theory of radiation and quanta". Max Planck received the 1918 Nobel Prize in Physics "in recognition of the services he rendered to the advancement of Physics by his discovery of energy quanta".
qas: answers: text: Rayleigh and Jeans
question: Einstein and what other two individuals revisited the black-body problem in 1905?

answers: text: Paul Ehrenfest
question: Who came up with the term, "ultraviolet catastrophe"?

answers: text: 1911
question: When did Paul Ehrenfest come up with the name "ultraviolet catastrophe"?

answers: text: 1911
question: When was the first Solvay Conference held?

answers: text: Max Planck
question: Who received the Nobel Prize in Physics in 1918?

answers: text: classical electromagnetism could never account for the observed spectrum
question: What did Rayleigh & Jeans and Einstein prove independently in 1905?

answers: text: the "ultraviolet catastrophe"
question: What name did Paul Ehrenfest give to the proofs from Einstein and Rayleigh & Jeans?

answers: text: 1911
question: When was the first Solvay Conference held?

answers: text: "the theory of radiation and quanta"
question: What was the topic of the first Solvay Conference?

answers: text: 1918
question: In what year did Planck receive the Nobel Prize in Physics for his discovery of energy quanta?

context: The photoelectric effect is the emission of electrons (called "photoelectrons") from a surface when light is shone on it. It was first observed by Alexandre Edmond Becquerel in 1839, although credit is usually reserved for Heinrich Hertz, who published the first thorough investigation in 1887. Another particularly thorough investigation was published by Philipp Lenard in 1902. Einstein's 1905 paper discussing the effect in terms of light quanta would earn him the Nobel Prize in 1921, when his predictions had been confirmed by the experimental work of Robert Andrews Millikan. The Nobel committee awarded the prize for his work on the photo-electric effect, rather than relativity, both because of a bias against purely theoretical physics not grounded in discovery or experiment, and dissent amongst its members as to the actual proof that relativity was real.
qas: answers: text: Alexandre Edmond Becquerel
question: Who first observed the photoelectric effect?

answers: text: 1839
question: When was the photoelectric effect first observed?

answers: text: Heinrich Hertz
question: Who published the first thorough investigation of the photoelectric effect?

answers: text: Einstein
question: Who received the Nobel Prize in 1921 for his work on the photoelectric effect?

answers: text: his work on the photo-electric effect
question: What did Einstein with the 1921 Nobel Prize for?

answers: text: the emission of electrons (called "photoelectrons") from a surface when light is shone on it
question: What is the photoelectric effect?

answers: text: Alexandre Edmond Becquerel
question: Who first observed the photoelectric effect?

answers: text: 1921
question: Einstein's paper on the photoelectric effect earned him the Nobel Prize in what year?

answers: text: relativity
question: Einstein's photoelectric effect work was rewards as opposed to his work on what other topic?

context: Prior to Einstein's paper, electromagnetic radiation such as visible light was considered to behave as a wave: hence the use of the terms "frequency" and "wavelength" to characterise different types of radiation. The energy transferred by a wave in a given time is called its intensity. The light from a theatre spotlight is more intense than the light from a domestic lightbulb; that is to say that the spotlight gives out more energy per unit time and per unit space(and hence consumes more electricity) than the ordinary bulb, even though the colour of the light might be very similar. Other waves, such as sound or the waves crashing against a seafront, also have their own intensity. However, the energy account of the photoelectric effect didn't seem to agree with the wave description of light.
qas: answers: text: a wave
question: Before Einstein, electromagnetic radiation was considered to behave as what?

answers: text: "frequency" and "wavelength"
question: What terms describe different types of radiation?

answers: text: sound
question: What other types of wave besides light has its own intensity?

answers: text: intensity
question: What is the energy transferred by a wave in a given time called?

answers: text: a wave
question: Prior to Einstein's work, light behavior was modeled as what?

answers: text: intensity
question: What is the name for the amount of energy transfered by a wave in a given time?

answers: text: the energy account
question: What portion of the photoelectric effect was in disagreement with the believed description of light behavior?

answers: text: gives out more energy per unit time and per unit space
question: What does it mean for a light source to be more intense than another?

context: The "photoelectrons" emitted as a result of the photoelectric effect have a certain kinetic energy, which can be measured. This kinetic energy (for each photoelectron) is independent of the intensity of the light, but depends linearly on the frequency; and if the frequency is too low (corresponding to a photon energy that is less than the work function of the material), no photoelectrons are emitted at all, unless a plurality of photons, whose energetic sum is greater than the energy of the photoelectrons, acts virtually simultaneously (multiphoton effect)  Assuming the frequency is high enough to cause the photoelectric effect, a rise in intensity of the light source causes more photoelectrons to be emitted with the same kinetic energy, rather than the same number of photoelectrons to be emitted with higher kinetic energy.
qas: answers: text: photoelectrons
question: What is emitted as a result of the photoelectric effect?

answers: text: the frequency
question: What does the kinetic energy of a photoelectron depend on?

answers: text: no photoelectrons are emitted at all
question: What happens if the photoelectron's frequency is too low?

answers: text: multiphoton effect
question: What is the term used when photoelectrons act virtually at the same time?

answers: text: kinetic
question: What type of energy due photoelectrons emitted due to the photoelectric effect have?

answers: text: frequency
question: What factor of the initial light source does the energy of the photoelectrons depend on?

answers: text: no photoelectrons are emitted at all
question: When the photon energy is less than the work function of the material the light is shone upon, how many photoelectrons are emitted?

answers: text: more photoelectrons to be emitted with the same kinetic energy
question: If the photoelectric effect is occuring, increasing the intensity of the light source causes what?

context: Niels Bohr introduced the first quantized model of the atom in 1913, in an attempt to overcome a major shortcoming of Rutherford's classical model. In classical electrodynamics, a charge moving in a circle should radiate electromagnetic radiation. If that charge were to be an electron orbiting a nucleus, the radiation would cause it to lose energy and spiral down into the nucleus. Bohr solved this paradox with explicit reference to Planck's work: an electron in a Bohr atom could only have certain defined energies En
qas: answers: text: Niels Bohr
question: Who introduced the first quantized model of the atom?

answers: text: 1913
question: When was the first quantized model of the atom introduced?

answers: text: to overcome a major shortcoming of Rutherford's classical model
question: Why was the first quantized model of the atom introduced?

answers: text: radiate electromagnetic radiation
question: In classical electrodynamics, a charge moving in a circle should do what?

answers: text: Niels Bohr
question: Who modeled the atom in 1913, challenging Rutherford's model?

answers: text: the radiation would cause it to lose energy and spiral down into the nucleus
question: What was predicted to happen to a nucleus-orbiting electron under Rutherford's model?

answers: text: an electron in a Bohr atom could only have certain defined energies
question: What statement did Bohr make about the electron of an atom, citing Planck's work?

context: Bohr also introduced the quantity , now known as the reduced Planck constant, as the quantum of angular momentum. At first, Bohr thought that this was the angular momentum of each electron in an atom: this proved incorrect and, despite developments by Sommerfeld and others, an accurate description of the electron angular momentum proved beyond the Bohr model. The correct quantization rules for electrons – in which the energy reduces to the Bohr model equation in the case of the hydrogen atom – were given by Heisenberg's matrix mechanics in 1925 and the Schrödinger wave equation in 1926: the reduced Planck constant remains the fundamental quantum of angular momentum. In modern terms, if J is the total angular momentum of a system with rotational invariance, and Jz the angular momentum measured along any given direction, these quantities can only take on the values
qas: answers: text: Bohr
question: Who introduced the reduced Planck constant?

answers: text: the quantity
question: What is the reduced Planck constant also known as?

answers: text: Heisenberg
question: Who helped to give the correct quantization rules for electrons in 1925?

answers: text: Schrödinger
question: Who helped to give the correct quantization rules for electrons in 1926?

answers: text: the fundamental quantum of angular momentum
question: According to Heisenberg and Schrödinger, the reduced Planck constant remains what?

answers: text: the reduced Planck constant
question: Bohr introduced what value as the quantum of angular momentum?

answers: text: Bohr thought that this was the angular momentum of each electron in an atom
question: What incorrect belief did Bohr hold about the reduced Planck constant?

answers: text: Heisenberg
question: What scientist used matrix mechanics to bring electron behavior in line with the Bohr model?

answers: text: 1926
question: When was the Schrödinger wave equation proposed?

context: where the uncertainty is given as the standard deviation of the measured value from its expected value. There are a number of other such pairs of physically measurable values which obey a similar rule. One example is time vs. energy. The either-or nature of uncertainty forces measurement attempts to choose between trade offs, and given that they are quanta, the trade offs often take the form of either-or (as in Fourier analysis), rather than the compromises and gray areas of time series analysis.
qas: answers: text: time vs. energy
question:  What measurable value obeys a similar rule of angular momentum?

answers: text: either-or nature of uncertainty
question: What forces measurement attempts to choose between trade-offs, in quanta?

answers: text: either-or (as in Fourier analysis)
question: What form do measurement attempt trade-offs for quanta take the form of?

answers: text: the standard deviation of the measured value from its expected value
question: How is uncertainly measured in this experience?

answers: text: Fourier analysis
question: What type of analysis fits the either-or nature of the uncertainty?

answers: text: time vs. energy
question: What example is given as another paired relationship of uncertainly related to standard deviation?

context: The Bohr magneton and the nuclear magneton are units which are used to describe the magnetic properties of the electron and atomic nuclei respectively. The Bohr magneton is the magnetic moment which would be expected for an electron if it behaved as a spinning charge according to classical electrodynamics. It is defined in terms of the reduced Planck constant, the elementary charge and the electron mass, all of which depend on the Planck constant: the final dependence on h1/2 (r2 > 0.995) can be found by expanding the variables.
qas: answers: text: Bohr magneton
question: What is the unit of magentic properties of the electron?

answers: text: nuclear magneton
question: What is the unit of magentic properties of atomic nuclei?

answers: text: behaved as a spinning charge according to classical electrodynamics
question: The Bohr magneton is the magnetic moment of an electron under what restriction?

answers: text: the reduced Planck constant, the elementary charge and the electron mass
question: What three terms define the Bohr magneton value?

context: In principle, the Planck constant could be determined by examining the spectrum of a black-body radiator or the kinetic energy of photoelectrons, and this is how its value was first calculated in the early twentieth century. In practice, these are no longer the most accurate methods. The CODATA value quoted here is based on three watt-balance measurements of KJ2RK and one inter-laboratory determination of the molar volume of silicon, but is mostly determined by a 2007 watt-balance measurement made at the U.S. National Institute of Standards and Technology (NIST). Five other measurements by three different methods were initially considered, but not included in the final refinement as they were too imprecise to affect the result.
qas: answers: text: the Planck constant could be determined by examining the spectrum of a black-body radiator or the kinetic energy of photoelectrons
question: How was the Planck constant calculated in the early 20th century?

answers: text: 2007
question: The value quoted here for the Planck constant is based on a measurement in what year?

answers: text: the U.S. National Institute of Standards and Technology (NIST)
question: Where was this measurement made?

answers: text: watt-balance measurement
question: What method was was used to obtain the measurement?

answers: text: silicon
question: One other measure involved the molar volume of what element?

context: There are both practical and theoretical difficulties in determining h. The practical difficulties can be illustrated by the fact that the two most accurate methods, the watt balance and the X-ray crystal density method, do not appear to agree with one another. The most likely reason is that the measurement uncertainty for one (or both) of the methods has been estimated too low – it is (or they are) not as precise as is currently believed – but for the time being there is no indication which method is at fault.
qas: answers: text: the two most accurate methods, the watt balance and the X-ray crystal density method, do not appear to agree with one another
question: What is a main practical difficulty in determining n?

answers: text: it is (or they are) not as precise as is currently believed
question: Why does this difficulty occur?

answers: text: there is no indication which method is at fault
question: Which method is at fault or the discrepancy?

context: The theoretical difficulties arise from the fact that all of the methods except the X-ray crystal density method rely on the theoretical basis of the Josephson effect and the quantum Hall effect. If these theories are slightly inaccurate – though there is no evidence at present to suggest they are – the methods would not give accurate values for the Planck constant. More importantly, the values of the Planck constant obtained in this way cannot be used as tests of the theories without falling into a circular argument. Fortunately, there are other statistical ways of testing the theories, and the theories have yet to be refuted.
qas: answers: text: the Josephson effect and the quantum Hall effect
question: Other than the X-ray crystal density method, other methods rely on what two effects?

answers: text: If these theories are slightly inaccurate
question: Why does relying on these effects create concern?

answers: text: a circular argument
question: Using Planck constant values from these effects would lead to what logical issue?

answers: text: there are other statistical ways of testing the theories, and the theories have yet to be refuted.
question: What is the saving grace of relying on these theories?

context: A watt balance is an instrument for comparing two powers, one of which is measured in SI watts and the other of which is measured in conventional electrical units. From the definition of the conventional watt W90, this gives a measure of the product KJ2RK in SI units, where RK is the von Klitzing constant which appears in the quantum Hall effect. If the theoretical treatments of the Josephson effect and the quantum Hall effect are valid, and in particular assuming that RK = h/e2, the measurement of KJ2RK is a direct determination of the Planck constant.
qas: answers: text: an instrument for comparing two powers, one of which is measured in SI watts and the other of which is measured in conventional electrical units
question: What is a watt balance?

answers: text: the von Klitzing constant which appears in the quantum Hall effect
question: What value does RK represent?

answers: text: the Planck constant
question: If the effects are valid, for RK = n/e2, what is the measurement of KJ2RK equal to?

context: The gyromagnetic ratio γ is the constant of proportionality between the frequency ν of nuclear magnetic resonance (or electron paramagnetic resonance for electrons) and the applied magnetic field B: ν = γB. It is difficult to measure gyromagnetic ratios precisely because of the difficulties in precisely measuring B, but the value for protons in water at 7002298150000000000♠25 °C is known to better than one part per million. The protons are said to be "shielded" from the applied magnetic field by the electrons in the water molecule, the same effect that gives rise to chemical shift in NMR spectroscopy, and this is indicated by a prime on the symbol for the gyromagnetic ratio, γ′p. The gyromagnetic ratio is related to the shielded proton magnetic moment μ′p, the spin number I (I = 1⁄2 for protons) and the reduced Planck constant.
qas: answers: text: the frequency ν of nuclear magnetic resonance
question: The gyromagnetic ratio is the constant proportion between the magentic field and what?

answers: text: The protons are said to be "shielded" from the applied magnetic field by the electrons in the water molecule
question: How does the water molecule impact the effect of magnetic fields on protons?

answers: text: related to the shielded proton magnetic moment μ′p, the spin number I (I = 1⁄2 for protons) and the reduced Planck constant.
question: What three factors impact the gyromagnetic ratio?

answers: text: the applied magnetic field B
question: The gyromagnetic ratio is often difficult to determine due to difficulty accurately determining the value of what?

context: A further complication is that the measurement of γ′p involves the measurement of an electric current: this is invariably measured in conventional amperes rather than in SI amperes, so a conversion factor is required. The symbol Γ′p-90 is used for the measured gyromagnetic ratio using conventional electrical units. In addition, there are two methods of measuring the value, a "low-field" method and a "high-field" method, and the conversion factors are different in the two cases. Only the high-field value Γ′p-90(hi) is of interest in determining the Planck constant.
qas: answers: text: there are two methods of measuring the value
question: How many methods of measuring the gyromagnetic ratio are there?

answers: text: the conversion factors are different in the two cases
question: How do conversion factors compare in "low-field" and "high-field" methods of measuring the gyromagnetic ratio?

answers: text: Only the high-field value Γ′p-90(hi) is of interest in determining the Planck constant
question: Which method is of interest in determining the Planck constant?

answers: text: electric current: this is invariably measured in conventional amperes rather than in SI amperes
question: Why is the measurement of electric current an issue in the estimate of the gyromagnetic ratio?

context: The Faraday constant F is the charge of one mole of electrons, equal to the Avogadro constant NA multiplied by the elementary charge e. It can be determined by careful electrolysis experiments, measuring the amount of silver dissolved from an electrode in a given time and for a given electric current. In practice, it is measured in conventional electrical units, and so given the symbol F90. Substituting the definitions of NA and e, and converting from conventional electrical units to SI units, gives the relation to the Planck constant.
qas: answers: text: the charge of one mole of electrons
question: What is the Faraday constant?

answers: text: by careful electrolysis experiments, measuring the amount of silver dissolved from an electrode in a given time and for a given electric current.
question: How is the Faraday constant determined?

answers: text: Substituting the definitions of NA and e, and converting from conventional electrical units to SI units, gives the relation to the Planck constant.
question: How does the Faraday constant relate to the Planck constant?

answers: text: the Avogadro constant NA multiplied by the elementary charge e
question: How is the Farday constant value quickly calculated?

context: The X-ray crystal density method is primarily a method for determining the Avogadro constant NA but as the Avogadro constant is related to the Planck constant it also determines a value for h. The principle behind the method is to determine NA as the ratio between the volume of the unit cell of a crystal, measured by X-ray crystallography, and the molar volume of the substance. Crystals of silicon are used, as they are available in high quality and purity by the technology developed for the semiconductor industry. The unit cell volume is calculated from the spacing between two crystal planes referred to as d220. The molar volume Vm(Si) requires a knowledge of the density of the crystal and the atomic weight of the silicon used. The Planck constant is given by
qas: answers: text: The X-ray crystal density method
question: What is the primary method for determining the Avogadro constant?

answers: text: the volume of the unit cell of a crystal, measured by X-ray crystallography, and the molar volume of the substance
question: The Avogadro constant is determined to be the ratio between what two factors in the X-ray crystal density method?

answers: text: Crystals of silicon
question: What element is used typically to establish Avogadro's constant?

answers: text: from the spacing between two crystal planes referred to as d220
question: How is unit cell volume calculated?

answers: text: the density of the crystal and the atomic weight of the silicon used
question: Calculating molar volume requires knowledge of what two factors?

context: There are a number of proposals to redefine certain of the SI base units in terms of fundamental physical constants. This has already been done for the metre, which is defined in terms of a fixed value of the speed of light. The most urgent unit on the list for redefinition is the kilogram, whose value has been fixed for all science (since 1889) by the mass of a small cylinder of platinum–iridium alloy kept in a vault just outside Paris. While nobody knows if the mass of the International Prototype Kilogram has changed since 1889 – the value 1 kg of its mass expressed in kilograms is by definition unchanged and therein lies one of the problems – it is known that over such a timescale the many similar Pt–Ir alloy cylinders kept in national laboratories around the world, have changed their relative mass by several tens of parts per million, however carefully they are stored, and the more so the more they have been taken out and used as mass standards. A change of several tens of micrograms in one kilogram is equivalent to the current uncertainty in the value of the Planck constant in SI units.
qas: answers: text: the kilogram
question: What measurement is deemed most important to redefine in terms of physical constants?

answers: text: cylinder
question: What is the shape of the object that establishes the base unit of the kilogram?

answers: text: platinum–iridium
question: What alloy is the base unit of the kilogram made from?

answers: text: in a vault just outside Paris
question: Where is the base unit for the kilogram kept?

context: The legal process to change the definition of the kilogram is already underway, but it had been decided that no final decision would be made before the next meeting of the General Conference on Weights and Measures in 2011. (For more detailed information, see kilogram definitions.) The Planck constant is a leading contender to form the basis of the new definition, although not the only one. Possible new definitions include "the mass of a body at rest whose equivalent energy equals the energy of photons whose frequencies sum to 7050135639273999999♠135639274×1042 Hz", or simply "the kilogram is defined so that the Planck constant equals 6966662606895999999♠6.62606896×10−34 J⋅s".
qas: answers: text: the General Conference on Weights and Measures in 2011
question: Where would the decision to change the definition of the kilogram have occured at the earliest?

answers: text: The Planck constant is a leading contender to form the basis of the new definition, although not the only one
question: Was the Planck constant the only option for redefining the kilogram?

answers: text: 7050135639273999999♠135639274×1042 Hz
question: The mass of a resting body with what energy would be equal to a kilogram?

answers: text: 6966662606895999999♠6.62606896×10−34 J⋅s
question: A kilogram could be definined as having a Planck constant of what value?