Key relationship
β=λD/d; I/I₁=4cos²(πy/β).
Physics · Class 12
Young double-slit fringes
Path difference changes across the screen. Constructive and destructive interference repeat at equal spatial intervals in the small-angle limit. Wavelength and screen distance broaden fringes; slit separation narrows them.
Open the interactive experiment →Young double-slit fringes
இரட்டைப் பிளவுகளில் பாதை வேறுபாடு மாறுவதால் ஒளி மற்றும் இருள் வரிகள் உருவாகும். வரி அகலம் λD/d ஆகும்.
Key notes, relationships and model limits
Remember
Path difference changes across the screen. Constructive and destructive interference repeat at equal spatial intervals in the small-angle limit. Wavelength and screen distance broaden fringes; slit separation narrows them.
Common trap
Fringe width differs from the central maximum width of a single slit.
Model limits
Equal coherent narrow slits; D≫d and small angles; diffraction envelope omitted to isolate interference spacing.
What you will learn
Predict interference-fringe spacing from apparatus dimensions.
Try the experiment
Try both scenarios, change one control, and predict the result before checking the graph and readouts.
Think of it this way
Change one input while keeping the others fixed, as you would in a controlled experiment.
Worked example
λ600 nm,D2 m,d0.5 mm gives β2.4 mm.
Why this matters
The model connects young double-slit fringes with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
Doubling slit separation changes fringe width to?
- Twice
- Half
- Unchanged
Read the explanation
β is inversely proportional to d.
Course connection: Class XII Chapter 10. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.