Planck's constant
Key Questions

Answer:
Planck's constant is instrumental and an unavoidable constant which appears in quantum mechanics.
Explanation:
Even though it was first introduced in the Planck's law,
#u_(lamda)d(lamda) = (8pihc)/lamda^5*(dlamda)/(e^((hc)/(lamdakT))1)# Where one quantum of radiation would have an energy,
#E = (hc)/(lamda)# , the concept of quantized radiation was extended by Einstein, later by Bohr in their theories as a part of the old quantum theory.Today almost all important relationships in quantum mechanics, contain Planck's constant (or the reduced Planck's constant
#h/(2pi)# ).Examples would include,
1) de Broglie relation 
#lamda = h/p# 2) Schrodinger equation 
#(ih)/(2pi)(delpsi)/(delt) = (h^2)/(8pi^2m)(nabla)^2psi + V(vec r,t)psi# 3) Commutator of
#x# and#p_x# #[x,p_x] = (ih)/(2pi)# And so on.
It is to quantum mechanics, what the constants
#epsilon_0# and#mu_0# are to Electricity and Magnetism. 
Answer:
Planck's constant is
#h~~6.63*10^34 \ "J"*"s"# .Explanation:
Planck's constant, in science, is denoted by
#h# , and is given the value of#h~~6.63*10^34 \ "J"*"s"# Note that
#1 \ "J"=1 \ "N"*"m"# #=1 \ "kg"*"m/s"^2*"m"# #=1 \ "kg"*"m"^2"/s"^2# And so, we can rewrite
#h# as#h~~6.63*10^34 \ "kg"*"m"^2"/s"^2*"s"# #=6.63*10^34 \ "kg"*"m"^2*"s"^1# This is one of the smallest constants in physics, and gives the relationship between a photon's energy and its frequency.