Q. Which one among the following has the highest energy? (UPSC Prelims 2009)
Answer: Blue light
Notes: Energy of light is directly proportional to its frequency and inversely proportional to its wavelength, as described by the equation E = hf (h being Planck's constant and f the frequency). Among visible light, blue light has the shortest wavelength and highest frequency, resulting in the greatest energy. Red light has the longest wavelength and lowest frequency. Therefore, blue light possesses the highest energy among these options.