Everything about Planck S Constant totally explained
The
Planck constant (denoted
) is a
physical constant that's used to describe the sizes of
quanta. It plays a central part in the theory of
quantum mechanics, and is named after
Max Planck, one of the founders of quantum theory. A closely related quantity is the
reduced Planck constant (also known as
Dirac's constant and denoted
, pronounced "h-bar"). The Planck constant is also used in measuring energy emitted as
photons, such as in the equation E=hf, where E is energy,
h is Planck's constant, and f is frequency.
The Planck constant and the reduced Planck constant are used to describe quantization, a phenomenon occurring in subatomic
particles such as
electrons and
photons in which certain physical properties occur in fixed amounts rather than assuming a continuous range of possible values.
Significance of the size of Planck's constant
Expressed in the
SI units of
joule seconds (J·s), the Planck constant is one of the smallest constants used in physics. The significance of this is that it reflects the extremely small scales at which quantum mechanical effects are observed, and hence why we're not familiar with quantum physics in our everyday lives in the way that we're with
classical physics. Indeed, classical physics can essentially be defined as the limit of quantum mechanics as the Planck constant tends to zero.
In
natural units, the Dirac constant is taken as 1 (
for example, the Planck constant is 2·π), as is convenient for describing physics at the atomic scale dominated by quantum effects.
Units, value and symbols
The Planck constant has dimensions of
energy multiplied by
time, which are also the dimensions of
action. In
SI units, the Planck constant is expressed in
joule seconds (J·s). The dimensions may also be written as
momentum times
distance (
N·
m·
s), which are also the dimensions of
angular momentum.
The value of the Planck constant is:
» , differs only from the Planck constant by a factor of
. The Planck constant is stated in
SI units of measurement, joules per
hertz, or joules per (
cycle per second), while the Dirac constant is the same value stated in joules per (
radian per second).
In essence, the Dirac constant is a conversion factor between
phase (in radians) and
action (in joule-seconds) as seen in the
Schrödinger equation. The Planck constant is similarly a conversion factor between phase (in cycles) and action. All other uses of Planck's constant and Dirac's constant follow from that relationship.
Further Information
Get more info on 'Planck S Constant'.
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