Which equation represents Planck's formula relating energy to frequency?

• A. E = hv
• B. E = hc/λ
• C. A = abc
• D. A = 2 - log%T

Answer: (A)

Energy is carried by a photon in discrete packets, and the size of that packet is proportional to its frequency. This direct relationship is given by E = hν, where h is Planck's constant. It explicitly links energy to frequency, which is what the question asks for. Planck's constant is a very small value, about 6.626×10^-34 J·s, setting the scale of photon energy.

If you instead express energy in terms of wavelength, you get E = hc/λ, using the fact that ν = c/λ. That form is equivalent but uses wavelength rather than frequency. The other options don’t describe photon energy in relation to frequency and are not valid formulas for this purpose.