7. Diffraction Flashcards
What is diffraction?
The way that waves spread out as they come through a narrow gap or go round obstacles
What does the amount of diffraction depend on?
The wavelength of the wave compared with the size of the gap
What happens when the gap is a lot bigger than the wavelength?
Diffraction is unnoticeable
What happens when the gap is several wavelengths wide?
Diffraction is noticeable
When does the most diffraction happen?
When the gap is the same size as the wavelength
What happens when the gap is smaller than the wavelength?
The waves are mostly just reflected back
What is meant by the shadow?
Where the wave is blocked by an obstacle
What causes a long shadow?
A wider obstacle than the wavelength of the wave
How can you observe a clear diffraction pattern?
Use a monochromatic, coherent light source
What is monochromatic light?
Light of a single wavelength and frequency and so is a single colour
What happens if you use light that isn’t monochromatic for observing diffraction patterns?
Different wavelengths will diffract different amounts and the pattern produced won’t be very clear
What are laser lights?
A monochromatic and coherent light source
Describe the pattern of single-slit diffraction for a laser light
- Has light and dark fringes
2. The central fringe is the brightest
What are the bright fringes a result of?
Constructive interference where waves from across the width of the slit arrive at the screen in phase
What are the dark fringes a result of?
Total destructive interference where waves from across the width of the slit arrive completely out of phase
Describe the pattern of single-slit diffraction for a white light
- The central fringe is white
- The light fringes are a spectrum of colours with red being the furthest from the centre because of their longer wavelength
Define the term intensity?
Intensity is the power per unit area
What is meant by the intensity of light?
The number of photons per unit area per second
What 2 things affect the width of the central maximum?
- Width of the slit
2. Wavelength of the light being diffracted
What happens to the width and intensity of the central maximum when the slit width increases?
The central maximum is narrower as a result of the lower amount of diffraction causing the intensity to be higher
What happens to the width and intensity of the central maximum when the wavelength increases?
The central maximum is wider as a result of the higher amount of diffraction causing the intensity to be lower
