Planck's constant value?

• A. 6.626 x 10^-34 Js
• B. 3.00 x 10^8 m/s
• C. 1.60 x 10^-19 C
• D. 9.81 m/s^2

Answer: (A)

Planck's constant sets the scale for quantum action and links energy to frequency through E = h f. Its value is about 6.626 × 10^-34 joule-seconds, which is why energies of photons are quantized in discrete multiples of h times the frequency. The units, joule-seconds, fit energy times time, matching how frequency (per second) combines with h to give energy. The other numbers are different constants: the speed of light, the elementary charge, and Earth's gravity. So the value that represents Planck's constant is 6.626 × 10^-34 J·s.