In a double-slit arrangement, if you double the slit separation d while keeping wavelength and distance to the screen fixed, what happens to the fringe spacing Δy?

In a double-slit arrangement, if you double the slit separation d while keeping wavelength and distance to the screen fixed, what happens to the fringe spacing Δy?

• A. Doubles
• B. Halves
• C. Remains the same
• D. Increases by a factor of four

Answer: (B)

In a double-slit setup, the spacing of the bright fringes on the screen is determined by how far apart successive bright maxima occur, and this spacing scales as Δy ≈ λ L / d when the angles are small. Here, λ (wavelength) and L (distance to the screen) are fixed, so Δy is inversely proportional to the slit separation d. If you double the slit separation, the spacing becomes Δy = λ L / (2d), which is half of the original. So the fringe spacing halves.

In a double-slit setup, the spacing of the bright fringes on the screen is determined by how far apart successive bright maxima occur, and this spacing scales as Δy ≈ λ L / d when the angles are small. Here, λ (wavelength) and L (distance to the screen) are fixed, so Δy is inversely proportional to the slit separation d. If you double the slit separation, the spacing becomes Δy = λ L / (2d), which is half of the original. So the fringe spacing halves.