Question

Observe the figure where three coloured lights are made to fall on a screen.

• [(a)] Which colours are labelled as A and D?
• [(b)] Among the colours A, B, C and D identify the primary colours and write down the colours.
• [(c)] There is a complementary colour pair among A, B, C and D. Pick them out and write down.

Hint:

RGB model: Red, Green, Blue → White
Complementary colours combine to give white light

Answer 1

Concept: Addition of Colours (RGB Model)
Primary colours of light: \[ \text{Red, Green, Blue} \] Their combinations produce:

• Red + Blue = Magenta
• Red + Green = Yellow
• Blue + Green = Cyan
• Red + Green + Blue = White

(a) Identify colours A and D
Step 1: From the diagram}
Given:

• One region is marked Red
• One region is Magenta (Red + Blue)
• Center is White (all three)

Step 2: Deduce remaining colours}
Thus: \[ A = \text{Green}, \quad D = \text{Blue} \] Conclusion (a): \[ A = \text{Green}, \quad D = \text{Blue} \] (b) Primary colours
Step 1: Primary colours of light}
\[ \text{Red, Green, Blue} \] Step 2: From labels}
\[ A = \text{Green}, \quad B = \text{Red}, \quad D = \text{Blue} \] Conclusion (b): \[ \text{Primary colours: Red, Green, Blue} \] (c) Complementary colour pair
Concept:
Complementary colours combine to form white light. Step 1: Identify pair}
\[ \text{Red + Cyan} = \text{White} \] \[ \text{Blue + Yellow} = \text{White} \] \[ \text{Green + Magenta} = \text{White} \] Step 2: From given labels}
Magenta is present, so: \[ \text{Green and Magenta} \] Conclusion (c): \[ \text{Complementary pair: Green and Magenta} \]