UPSC Prelims 2007 Q106: Science & Technology – Physics
Consider the following statements :
1. If magenta and yellow coloured circles intersect, the intersected area will have red colour.
2. If cyan and magenta coloured circles intersect, the intersected area will have blue colour.
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (c) Both 1 and 2
Explanation
Subtractive colour mixing (pigments / filters)
Primary subtractive colours: Cyan, Magenta, Yellow (CMY).
Each absorbs one additive primary:
| Colour | Absorbs | Lets through |
|---|---|---|
| Cyan | Red | Green + Blue |
| Magenta | Green | Red + Blue |
| Yellow | Blue | Red + Green |
Statement 1: Magenta + Yellow → common colour passed = Red — TRUE.
Statement 2: Cyan + Magenta → common colour passed = Blue — TRUE.
(Also: Cyan + Yellow → Green; all three → Black.)
Answer: (c) Both 1 and 2.
Why each option is right or wrong
- (a) Incorrect. Statement 2 is also true — cyan + magenta gives blue.
- (b) Incorrect. Statement 1 is also true — magenta + yellow gives red.
- (c) CORRECT. Magenta + Yellow = Red; Cyan + Magenta = Blue.
- (d) Incorrect. Both statements follow subtractive mixing rules.
Key point
Subtractive (CMY): M+Y = Red; C+M = Blue; C+Y = Green; C+M+Y = Black.
Remember
Magenta + Yellow = Red; Cyan + Magenta = Blue.
Common mistakes
- Using additive (light) rules instead — in light, red + green = yellow, which is the reverse direction.
- Thinking magenta + yellow gives orange — in ideal subtractive mixing it gives red.
- Forgetting that printers use CMYK (K = black) for this reason.
Exam tip
Each subtractive colour = 'white minus one'. Find the colour both let through: M (R+B) ∩ Y (R+G) = R.
Sources
- NCERT Class X — Science, Ch 11 (Human Eye and Colourful World)
- NCERT Class XII — Physics Part II, Ch 9 (Ray Optics)