Which equation represents energy using Planck's constant?

The equation that correctly represents energy using Planck's constant is E = h • f, where E represents energy, h is Planck's constant, and f is the frequency of the electromagnetic radiation. This relationship is foundational in quantum mechanics and describes how the energy of a photon is directly proportional to its frequency.

As frequency increases, the energy of the photon also increases, which is captured in this equation. Planck's constant (approximately 6.626 x 10^-34 J·s) serves as the proportionality factor that links the two quantities.

Using this equation, if you know the frequency of a photon, you can calculate its energy by multiplying that frequency by Planck's constant. This is particularly important in contexts such as photoelectric effects, where the energy of light is necessary to eject electrons from a material.

The other options represent incorrect formulations of energy in relation to Planck's constant or frequency, which does not align with established physics. For instance, the sum in one option and the squared term in another do not conform to the principles underpinning photon energy calculations. Thus, the equation E = h • f accurately captures the relationship between energy and frequency through Planck's constant.