Light from a helium-neon laser (λ = 633 nm) passes through a circular aperture and is observed on a screen 4.0 m behind the aperture. The width of the central maximum is 2.5 cm. What is the diameter (in mm) of the hole?
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34. Wave Optics
Single Slit Diffraction
Problem 6
Textbook Question
Monochromatic light of wavelength 633 nm falls on a slit. If the angle between the first bright fringes on either side of the central maximum is 32°, estimate the slit width.

1
Identify the relevant formula for single-slit diffraction. The angular position of the minima in a single-slit diffraction pattern is given by: , where is the slit width, is the angle to the m-th minimum, is the order of the minimum, and is the wavelength of the light.
Recognize that the problem provides the total angle between the first bright fringes on either side of the central maximum as 32°. This means the angle to the first minimum on one side of the central maximum is half of this value: .
Substitute the known values into the formula. For the first minimum, , , and . The equation becomes: .
Rearrange the equation to solve for the slit width : .
Use a calculator to compute and substitute it into the equation to find the value of . Ensure the angle is in degrees when calculating the sine function.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Diffraction
Diffraction is the bending of waves around obstacles and the spreading of waves when they pass through narrow openings. In the context of light, diffraction patterns are created when light waves encounter a slit, leading to the formation of bright and dark fringes on a screen. The extent of diffraction depends on the wavelength of the light and the size of the slit.
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Diffraction
Young's Double Slit Experiment
Young's Double Slit Experiment demonstrates the wave nature of light through the interference pattern created by two closely spaced slits. The positions of the bright and dark fringes are determined by the path difference between light waves emanating from the slits. This experiment is foundational in understanding how light behaves as a wave, particularly in terms of constructive and destructive interference.
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Young's Double Slit Experiment
Slit Width and Wavelength Relationship
The relationship between slit width, wavelength, and the angle of diffraction is described by the formula for single-slit diffraction. The width of the slit affects the angle at which the first bright fringe appears; narrower slits produce wider diffraction patterns. This relationship is crucial for calculating the slit width when given the wavelength of light and the angular separation of the fringes.
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Unknown Wavelength of Laser through Double Slit
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