Question

In Young's double-slit experiment, light was first passed through a narrow single slit before going on to the double-slits. The reason for the first slit was?

1) to ensure a constant phase relationship between the interfering light waves.
2) to reduce the brightness of the light so the interference pattern could be seen.
3) to polarize the light.
4) to screen out all wavelengths except those in the visible light spectrum.

Answer 1

The first slit in Young's double-slit experiment was used to make the light waves coherent, ensuring a constant phase relationship necessary for observable interference patterns.

to ensure a constant phase relationship between the interfering light waves.

Step-by-step explanation:

In Young's double-slit experiment, light was first passed through a single narrow slit before it reached the double slits. The purpose of this initial slit was to ensure that the light waves had a constant phase relationship between them, making them somewhat coherent.

Coherence is essential for creating an observable interference pattern, as it aligns the phases of light waves so they can interfere constructively or destructively when they pass through the double slits. The double slits then act as two coherent light sources that produce the interference pattern observed on the screen.

When Young used sunlight, each wavelength formed its own interference pattern, which made the overall effect more challenging to discern. To clarify the phenomenon, monochromatic light, which has a single wavelength, is often used in demonstrations of this experiment.