You should use the Physical Constants Package by using

<< PhysicalConstants`

When you enter now

PlanckConstant

you directly get the Plack Constant. With

PlanckConstant/(Joule Second)

you geht the Planck Constant without units.

You should use the Physical Constants Package by using

<< PhysicalConstants`

When you enter now

PlanckConstant

you directly get the Planck Constant. With

PlanckConstant/(Joule Second)

you get the Planck Constant without units.