What does Planck's equation (E=hf) calculate when given frequency?

Planck's equation, expressed as E = hf, is fundamental in quantum mechanics and relates the energy (E) of a photon to its frequency (f), with h representing Planck's constant. When frequency is provided, Planck's equation allows for the direct calculation of the energy of that photon. This relationship signifies that a photon’s energy is directly proportional to its frequency; as the frequency increases, so does the energy of the photon.

The energy calculated through Planck's equation is crucial in numerous applications, including understanding phenomena like the photoelectric effect, where photons can eject electrons from materials, demonstrating the quantized nature of light.

Other options, such as the speed of light, wavelength of an electron, and mass of a photon, do not directly relate to the function of Planck's equation. The speed of light is a constant value in physics that does not change with frequency. Wavelength calculations involve the speed of light and frequency but are not derived from Planck's equation. Additionally, while mass can be related to energy through Einstein's theory of relativity, Planck's equation specifically does not compute mass.