How does slit width affect diffraction patterns?

Slit width directly affects the diffraction pattern by determining the spread and intensity of the diffracted light.

In a diffraction experiment, light passes through a slit and spreads out, creating a pattern on a screen. This pattern is characterised by a central bright fringe (maximum) surrounded by alternating dark and bright fringes. The width of the slit plays a crucial role in determining the characteristics of this pattern.

When the slit width is decreased, the diffraction pattern spreads out more. This is because the wavefronts of light have a larger area to diffract into, leading to a wider spread of light. Conversely, if the slit width is increased, the diffraction pattern becomes narrower. This is due to the smaller area available for the wavefronts to diffract into, resulting in a more concentrated spread of light.

The intensity of the diffraction pattern is also affected by the slit width. A narrower slit allows less light to pass through, resulting in a less intense or dimmer central maximum. On the other hand, a wider slit allows more light to pass through, leading to a brighter central maximum. However, the intensity of the secondary maxima (the bright fringes surrounding the central maximum) decreases as the slit width increases. This is because more light is concentrated in the central maximum, leaving less light for the secondary maxima.

The slit width also affects the resolution of the diffraction pattern. A narrower slit provides a higher resolution, as it produces a wider diffraction pattern with more clearly separated fringes. This allows for more precise measurements and observations. Conversely, a wider slit produces a narrower diffraction pattern with less clearly separated fringes, resulting in lower resolution.

IB Physics Tutor Summary: The width of a slit affects how light spreads and the brightness of the diffraction pattern seen on a screen. A narrower slit makes the light spread more and the central bright area less intense, while a wider slit does the opposite. Also, a narrower slit means better detail in the pattern, allowing for more precise measurements.