Which equation is used to calculate energy in relation to frequency?

The equation used to calculate energy in relation to frequency is E = hv. In this equation, E represents energy, h is Planck's constant (approximately 6.626 x 10⁻³⁴ Joule seconds), and v (or ν) represents the frequency of the electromagnetic wave.

This relationship indicates that the energy of a photon is directly proportional to its frequency; as frequency increases, the energy of the photon also increases. This is a fundamental concept in quantum mechanics and is particularly relevant in understanding phenomena such as the photoelectric effect and the behavior of light as both a wave and a particle.

In contrast, the other equations provided do not relate energy directly to frequency. E = mc² is the famous equation from Einstein's theory of relativity, which relates mass and energy. E = h/c does not represent a direct relation based on frequency, as it combines Planck's constant and the speed of light (c) in a different context. Meanwhile, E = cY does not align with established physical principles regarding energy and frequency. Thus, E = hv is the only equation that accurately describes this relationship.