Practice portal › Dual Nature of Matter and Radiation › Photon Energy, Number of Photons and Intensity
Asked in GSEB Board July 2015 · Units and dimensions
Given: Planck's constant h.
Idea: get [h] from E=h u, so h=E/u.
[E]=M¹L²T⁻² and [ u]=T⁻¹, so [h]=M¹L²T⁻¹ -- in SI, J s.
Now take angular momentum, L=mvr: [L]=M¹×L¹T⁻¹×L¹=M¹L²T⁻¹ -- identical.
This is why Bohr's quantisation condition can be written mvr=(nh)/(2π): an equation only balances if both sides are quantities of the same kind.
So it is angular momentum that has the dimension of Planck's constant.
Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.
Practise this with a timer