The value of Planck's constant is

Question

Accepted Answer

1. **Definition:** Planck's constant ($h$) relates the energy of a photon ($E$) to its frequency ($
u$) via the equation $E = h
u$ .
2. **Value:** The accepted value of Planck's constant is approximately $6.626 	imes 10^{-34}$ J s , , , . In the context of the question, this is rounded to $6.63 	imes 10^{-34}$.
3. **Units:** Rearranging the equation to $h = E/
u$, the units are Energy $	imes$ Time (since frequency is $1/	ext{Time}$). The SI unit of energy is Joule (J) and time is Second (s). Therefore, the unit is Joule-second (J s or J-sec) .
4. **Dimensional Analysis:** The dimensional formula is $[ML^2T^{-1}]$, which corresponds to the unit $kg \cdot m^2 \cdot s^{-1}$. Option C ($kg\cdot m^2$) is dimensionally incorrect as it lacks the per second ($s^{-1}$) factor.
5. **Conclusion:** The correct value and unit combination is $6.63 	imes 10^{-34}$ J-sec.

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