Intelligent assessment and revision tools for OCR A Physics

Two monochromatic LEDs each illuminate the same small photodiode with equal intensity (same power per unit area). LED G emits green light at wavelength 500 nm; LED V emits violet light at 400 nm. Which statement must be true about the photon arrival rates at the diode, and why?

• A Both beams deliver the same number of photons per second because their intensities are equal.
• B The 400 nm beam delivers about 25% more photons per second because shorter-wavelength light arrives more frequently.
• C The 400 nm beam delivers about 20% fewer photons per second because each photon carries more energy at that wavelength.
• D The 500 nm beam delivers about 20% fewer photons per second because longer-wavelength photons travel more slowly to the detector.