State the principle of superposition of waves.
An arrangement is set up to demonstrate the interference of monochromatic light.
Coherent green light from a laser is incident at a double-slit. The separation between the slits is 0.40 mm0.40\text{ mm}0.40 mm. A series of dark and bright lines (fringes) appear on the screen. The screen is 3.20 m3.20\text{ m}3.20 m from the slits. A high-resolution digital sensor measures the fringe pattern shown above.
Use the diagram and measurements (where the center of the 2nd bright fringe is aligned with the 18.0 mm18.0\text{ mm}18.0 mm mark and the center of the 12th bright fringe is aligned with the 61.0 mm61.0\text{ mm}61.0 mm mark) to determine accurately the wavelength of the green light from the laser.
The green light is now replaced by a similar beam of blue light. State and explain the effect, if any, on the spacing of the fringes observed on the screen.
