A Level Physics Practice Exam

What is the formula for calculating the wavelength of a photon?

1. wavelength = c / E

2. wavelength = E / h

3. wavelength = c / f

4. wavelength = ch / E

The correct answer is: wavelength = ch / E

The correct formula for calculating the wavelength of a photon is given by the relationship between the speed of light, frequency, and wavelength. The formula is: wavelength = c / f where \( c \) is the speed of light and \( f \) is the frequency of the photon. This equation stems from the wave nature of light, establishing that the wavelength is inversely proportional to the frequency for a given medium, in this case, a vacuum. The relationship between energy and wavelength can also be used, as the energy \( E \) of a photon is related to its frequency by the formula \( E = hf \), where \( h \) is Planck's constant. By re-arranging this equation and using it to find the wavelength, we can derive that: wavelength = h / (E / c) However, the correct and straightforward way to calculate wavelength directly relates \( c \) and frequency as stated earlier. The other choices do not accurately represent the relationships needed to determine a photon's wavelength. For instance, option D, although similar to a relationship involving Planck's constant, does not provide the correct formula. By understanding these fundamental equations, one can effectively determine the wavelength of a photon based on its