Glossary
Central bright fringe
The widest and most intense bright band located directly in the center of a single-slit diffraction pattern.
Example:
In a single-slit diffraction pattern, the central bright fringe is always twice as wide as any other bright fringe.
Circular openings
A type of aperture that produces a diffraction pattern consisting of concentric bright and dark rings, known as an Airy pattern.
Example:
When light from a distant star passes through the circular aperture of a telescope, it forms an Airy disk due to diffraction from the circular opening.
Constructive interference
Occurs when two waves meet in phase, meaning their crests align with crests and troughs with troughs, resulting in a larger amplitude.
Example:
In a double-slit experiment, the bright bands on the screen are formed where light waves undergo constructive interference.
Destructive interference
Occurs when two waves meet out of phase, meaning the crest of one wave aligns with the trough of another, resulting in a smaller or zero amplitude.
Example:
Noise-canceling headphones work by generating sound waves that undergo destructive interference with incoming ambient noise, effectively silencing it.
Diffraction
The phenomenon where a wave spreads out as it passes through an opening or around an obstacle, causing it to bend around corners.
Example:
When sound waves from a concert travel around a large building, allowing you to hear the music even if you're not in direct line of sight, this is an example of sound diffraction.
Diffraction gratings
An optical component with a large number of closely spaced parallel lines or grooves, used to separate light into its constituent wavelengths by diffraction and interference.
Example:
Spectrometers use diffraction gratings to split white light into a clear spectrum of colors, allowing scientists to analyze the composition of light sources.
Distance to screen (L)
The measurement from the diffracting opening to the screen where the interference pattern is observed.
Example:
Increasing the distance to screen (L) makes the bright and dark fringes in a diffraction pattern appear further apart, making them easier to measure.
Double slits
An experimental setup involving two closely spaced parallel slits, which produces an interference pattern characterized by evenly spaced bright fringes with varying intensity modulated by a single-slit diffraction envelope.
Example:
Thomas Young's famous experiment used double slits to demonstrate the wave nature of light by observing the distinct interference pattern.
Fringes
The alternating bright and dark bands or regions observed in an interference or diffraction pattern.
Example:
The distinct colored bands seen when light reflects off a soap bubble are an example of interference fringes.
Interfere
When two or more waves superimpose to form a resultant wave of greater, lower, or the same amplitude.
Example:
When ripples from two stones dropped in a pond meet, they interfere with each other, creating a complex pattern of peaks and troughs.
Interference pattern
The characteristic pattern of alternating bright and dark regions (or loud and quiet regions for sound) formed when waves interfere.
Example:
The colorful swirls seen on a thin film of oil on water are a beautiful example of an interference pattern created by light reflecting off the top and bottom surfaces.
Monochromatic light
Light of a single wavelength or color, often used in diffraction and interference experiments to produce clear patterns.
Example:
A laser pointer emits monochromatic light, which is why it produces a very distinct and sharp diffraction pattern when shone through a narrow slit.
Obstacle
A physical barrier or object that a wave encounters, causing it to diffract around its edges.
Example:
A large rock in a river acts as an obstacle, causing water ripples to spread out behind it.
Opening
A gap or aperture through which a wave passes, leading to the spreading out of the wave as it exits.
Example:
Light passing through a tiny pinhole creates a blurry, spread-out spot on a screen, demonstrating diffraction through an opening.
Order of the minimum (m)
An integer (1, 2, 3...) that identifies the specific dark fringe (minimum brightness) away from the central maximum in a diffraction pattern.
Example:
The first dark band on either side of the central bright fringe corresponds to the order of the minimum (m) = 1.
Path length difference (ΔD)
The difference in the distance traveled by two waves from their source to a specific point, which determines whether they interfere constructively or destructively.
Example:
For destructive interference to occur at a point, the path length difference (ΔD) between two waves arriving there must be an odd multiple of half a wavelength.
Rectangular slits
A common type of opening, typically a long, narrow rectangle, used to produce a diffraction pattern of alternating bright and dark bands.
Example:
Most introductory physics experiments on single-slit diffraction use rectangular slits to demonstrate the characteristic bright and dark fringe pattern.
Slit width (a)
The physical width of the narrow opening through which light or other waves pass in a diffraction experiment.
Example:
Decreasing the slit width (a) in a single-slit experiment causes the central bright fringe to spread out more, indicating greater diffraction.
Small angle approximation
A mathematical simplification where for small angles (typically less than 10 degrees), $\sin\theta \approx \tan\theta \approx \theta$ (in radians).
Example:
When analyzing the spacing of fringes in a diffraction pattern on a distant screen, the small angle approximation simplifies calculations by allowing us to use instead of .
Wave nature of light and matter
The principle that light and matter (like electrons) exhibit properties of both waves and particles, demonstrating phenomena like diffraction and interference.
Example:
The observation of electron diffraction patterns through a crystal provides strong evidence for the wave nature of light and matter, showing electrons behave like waves.
Wavelength
The spatial period of a periodic wave, the distance over which the wave's shape repeats.
Example:
Radio waves have very long wavelengths, which is why they can easily diffract around hills and buildings.