physics: when pure red light is directed to a green leaf, what will be the colour of the leaf?

Question

the truth answer is yellow (according to the quiz master's answer), but according to physics' theory, it's black since red light will be absorbed by green things. i didn't get to experiment it myself.

is this question related to biology and chemistry, beside physics, since it involves the 'leaf'?

please explain in detail.

i'm dying for an explaination. thanks. ^_^

thanks for the answers, but i don' t understand a few, especially anami's and orange's (my english isn't very good). please explain it more lengthily and plz use very simple english.

added question to orange's answer: why does the leaf radiate light waves in the dark?

plz add in the site (if any) where i can find very detailed and theory answer to the question.

thanks for the trouble.

Answer 1

The leaf would appear black as green leaves absorbs all other lights than the green one. But in a room illumunated with red light it will absob the red light too, reflecting no lightwaves so it will appear black.



Answer of Details section: - I later thought about your question. & came to the conclusion that as far as my knowledge goes you were right & the quizmaster must have committed any mistake.

When a body is exposed to any kind of radiation ( sunlight is also a kind of radiation. Ain't it? Light radiation) , it absorbs energies ( ie waves) of some definite waveleghts. [ Sodium (Na) absorbs yellow light under proper circumstances.] . This energy which is absorbed by them is radiated when they are excited by proper means.[ consider Black body radiation in case of Heat radiation. It is the same as that]. so the leaf will radiate all lightwaves of solar spectrum except the green one. All that is fine.

But I think the conclusion I drew on this basis was faulty. Later on I found in books that those lightwaves togetherly do not generate green light. So I think the leaf will appear black. There is no role of the radiation from the leaf itself. You were most probably correct.

Answer 2

The yellow answer mistakenly assumed that the reflected light would be intermediate in wavelength between green and red. Non-luminous objects, by definition, do not emit their own light; they only reflect light they are exposed to. The color of an opaque non-luminous object is determined by which wavelengths have the highest reflectivity of incident light. If an object's color was perfectly green, for example, it would reflect *only* green light, and absorb all other wavelengths. That means if it were exposed to red light, it would appear black. Black is what happens when an object absorbs (does not reflect) light it's exposed to. However, few objects are perfectly pure in color. A real leaf, for example, will reflect some red; The red in normal (white) light is just drowned out by the higher reflecting green. However, if the light it's exposed to is pure red, then red is all that it can reflect. If it reflects any red at all, it will appear red. If it only reflects a little red, it will look dark red. An oak leaf, though, actually reflects a lot of red. It gives the leaf a distinctive hue and, in the fall when the (green) chlorophyll dies, beautiful red it all you see.

Answer 3

was the leaf pluck off the tree . plants love pure red light its lets them grow better biology is part of the answer once a leaf is off tree its lifeless a leaf on tree would react better by putting it self to the red light i know that red and green turns yellow in most cases but not always true when it comes to a living specimen

Answer 4

It will be black. If there are no other lights in the room, then it will be black. A material will absorb certain wavelengths and reflect others. These reflections are the colors that we see. I myself have seen a red apple under a green light and it was relatively black (there were a few green spots). It doesn't have much to do with biology; It could be a green ball.

Answer 5

See all objects reflect all colors except 1 but bio says due to chlorophyll its green so the chlorophyll must reflect all colors except green and so the leaf is green Happy to help Kodester

Answer 6

visible spectrum : VIB...GYOR
now here the leaf is green i.e. emitting light of wavelengths which are in green part of visible spectrum. when pure red falls on it then the two wavelengths will superimpose to give general illumination of a wavelength average of two and it happens to be yellow

Answer 7

i would also say black since chlorophylla absorb red

Answer 8

black