Like sound waves, light waves and microwaves can interfere. This interference can be observed by shining a single light source through two thin vertical slits, an arrangement known as a double slit.
The phenomenon was first observed by English physicist and physician Thomas Young in 1801 and is known as double-slit interference or Young's slit experiment.
How does it work?
When a laser or lamp is used to shine light through the two slits, light falls on both slits and creates diffraction patterns.
If a laser is used, the light is already coherent, meaning the waves are in phase.
If a lamp is used, a single slit is placed before the double slit, making the light coherent by allowing only a small portion of the wavefront to pass through.
Each slit emits a cone of diffracted light, which is bounded by the central maximum of the diffraction pattern for that cone.
The region where the two diffracted beams intersect is where interference can occur. This is because interference requires two beams.
Interference pattern
When a screen is placed parallel to the plane of the slits in the interference region, a pattern of fringes appears on the screen.
These fringes, parallel to the orientation of the double slits, show an alternating bright–dark arrangement with equal spacing on the screen.
This pattern is similar to the alternating loud and soft regions of sound wave interference.
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Theme C - Wave Behaviour
Unlocking Light Mysteries: The Double-Slit Experiment
Like sound waves, light waves and microwaves can interfere. This interference can be observed by shining a single light source through two thin vertical slits, an arrangement known as a double slit.
The phenomenon was first observed by English physicist and physician Thomas Young in 1801 and is known as double-slit interference or Young's slit experiment.
How does it work?
When a laser or lamp is used to shine light through the two slits, light falls on both slits and creates diffraction patterns.
If a laser is used, the light is already coherent, meaning the waves are in phase.
If a lamp is used, a single slit is placed before the double slit, making the light coherent by allowing only a small portion of the wavefront to pass through.
Each slit emits a cone of diffracted light, which is bounded by the central maximum of the diffraction pattern for that cone.
The region where the two diffracted beams intersect is where interference can occur. This is because interference requires two beams.
Interference pattern
When a screen is placed parallel to the plane of the slits in the interference region, a pattern of fringes appears on the screen.
These fringes, parallel to the orientation of the double slits, show an alternating bright–dark arrangement with equal spacing on the screen.
This pattern is similar to the alternating loud and soft regions of sound wave interference.
Unlock the Full Content!
Dive deeper and gain exclusive access to premium files of Physics HL. Subscribe now and get closer to that 45 🌟