In a Young's double slit experiment, the source is white light. One of the slits is covered by red filter and another by a green filter. In this case:

 

🌈 YDSE with Red and Green Filters – Interference of Light | JEE Physics | Doubtify

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📌 Question:

In a Young's double slit experiment (YDSE), the source is white light. One of the slits is covered by a red filter and the other by a green filter. What will be observed?

Options:

1. There shall be an interference pattern for red distinct from that for green.

2. There shall be an interference pattern, where each fringe’s pattern center is green and outer edges is red.

3. There shall be no interference fringes.

4. There shall be alternate interference fringes of red and green.

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🖼️ Question Image:

🧠 Solution Image:

🔬 Concept Explanation:

In Young’s Double Slit Experiment, interference fringes are formed only when the light waves from both slits are coherent – i.e., they have:

• The same wavelength

• Constant phase difference

But in this case:

• One slit passes red light (≈700 nm)

• The other passes green light (≈550 nm)

👉 These lights have different wavelengths, different frequencies, and no fixed phase relationship.
Hence, they are not coherent.

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❌ So, what happens?

• No interference occurs between red and green lights.

• The overlapping of two incoherent light waves only leads to a uniform intensity pattern, not interference fringes.

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✅ Final Answer:

Option 3: There shall be no interference fringes.

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🎯 Why This Question Is Important:

• Tests deep understanding of wave nature of light

• Checks your conceptual clarity on conditions for interference

• Very common JEE trap question – looks tricky but based on a simple principle

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🧠 Pro Tip:

Filters remove all other wavelengths from white light except the color they represent. So in this setup, both slits are passing different monochromatic lights, leading to no fixed phase relationship → no interference.

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