What is the function of a coloured filter?

A coloured filter functions by selectively allowing certain wavelengths (or colors) of light to pass through while absorbing others. When white light, which consists of a combination of all colors, passes through a coloured filter, the filter absorbs specific wavelengths corresponding to the colors it is designed to block. The remaining light that comes through is composed of the wavelengths that are transmitted, producing a light that appears to be the color of the filter. This is why option C is the correct choice.

Understanding how filters work is crucial in optics. For instance, if you have a red filter, it will absorb green, blue, and yellow light, while allowing red light to pass through. Therefore, the light that emerges from the filter will predominantly be red. This concept is foundational in various applications, such as photography and stage lighting, where controlling the color of light is essential.