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Color Filters - help10

A color filter will selectively absorb a range of light colors. That is, specific colors of light are blocked by the filter and not allowed to pass through. The colors of light that approach the filter and are not blocked (or absorbed) will be transmitted through the filter and illuminate the screen. It is the transmitted light that affects the color of the screen.

There are two similar versions of this question. Here is one of those versions:

Version 1:

Magenta light is incident upon two different color filters. The light passing through the filters and illuminates a white screen. What will be the color appearance of the screen?

Vocabulary Terms
Let's begin with some vocabulary terms that you should become acquainted with:

Incident: incident means to approach. Incident light is light that is approaching a filter. You will need to pay attention to the light that is incident on the first filter.

Absorb: color filters absorb or block light of a given color. A red filter absorbs cyan light (i.e., blue and green light). Blue and green light will never pass through a red filter.

Transmit: transmit means to pass through or across. The lightcolor(s) that does not get absorbed will be transmitted.

Using the Incident-Absorbed-Transmitted Model
A useful model for analyzing color filter questions is what we call the incident-absorbed-reflected model. The model suggests that a successful analysis includes three steps ... with each step involving the answering of a question. Those steps or questions are ...

What color(s) of light are incident on the filter?
Of the light colors that are incident, which color(s) is/are absorbed by the filter?
Of the light colors that are incident, which color(s) is/are transmitted through the filter?

The color(s) of light that is/are absorbed is/are subtracted from the color of light that are incident upon the filter. Once the subtraction process is complete, the result is the transmitted light color.

In this question, magenta light (a.k.a., red and blue light) are incident upon the filter. The first filter is a magenta filter. Magenta filters absorb green light (when present) and let red and blue light pass through. So the color Green would be subtracted from the Red and Blue incident light if it were present. The fact that green is not incident on the first filter means that we don't have to worry about subracting it. So Red and Blue light is being transmitted through the first filter and is incident towards the second filter. The second filter is a yellow filter. Yellow filters absorb blue light and allow (if present) red and green light to pass through. So the color Blue must be subtracted from the Red and Blue. This leaves Red light being transmitted through the second filter and approaching the screen. Red light will thus be shining on the screen and will determine the screen's color. The color subtraction equation can be written as ...

RB - 0 - B = R
(The 0 means no light is subtracted.)

Try this link to The Physics Classroom Tutorial for more help with the understanding how filters interact with the incident light:

Color Subtraction