A Level Physics Practice Exam

How can the energy of a photon be expressed in terms of its wavelength?

1. E = mc^2

2. E = hf

3. E = h / wavelength

4. E = mc^3

The correct answer is: E = hf

The energy of a photon can be expressed in terms of its wavelength using the equation derived from the relationship between energy, frequency, and wavelength. The correct expression for the energy of a photon is given by the equation E = hf, where E represents the energy, h is Planck's constant, and f is the frequency of the photon. To connect frequency to wavelength, one can use the wave equation, which states that the speed of light (c) is equal to the product of its frequency (f) and wavelength (λ): c = fλ. By rearranging this equation, we can express frequency as f = c / λ. Substituting this back into the equation for energy gives us E = h(c / λ), which can also be written as E = hc / λ. Thus, energy is inversely proportional to the wavelength. This explains why the expression for energy in terms of wavelength is derived and how it fundamentally relates to other properties of light, allowing us to understand that shorter wavelengths correspond to higher energy photons.