There are a LOT of stamps featuring Albert Einstein, from a variety of countries, This one is both decorative and informative, illustrating the photoelectric effect. Einstein’s discovery of the law of photoelectric effect in 1905 was a major contributing factor to his winning of the Nobel Prize for Physics in 1921.
Frequent visitors to this site will know that I am not a scientist. So the lengthy description of the photoelectric effect on the second link below consists of a bunch of words that I understand individually but fail to understand in combination. I’ll keep staring at them thought because I’m fascinated by all things that I don’t understand…
https://en.wikipedia.org/wiki/Einstein%27s_awards_and_honors
Stamp of the Day 