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Coherent light with wavelength 450 nm falls on a pair of slits. On a screen 1.80 m away, the distance between dark fringes is 3.90 mm. What is the slit separation?

Short Answer

Expert verified
The slit separation is approximately 2.08 x 10^{-4} m.

Step by step solution

01

Understand the Concept

The problem involves two-slit interference. The formula for the position of dark fringes in a double-slit experiment is given by: \[ d \sin \theta = (m + \frac{1}{2}) \lambda \] where \( d \) is the slit separation, \( \theta \) is the angle of the fringe, \( m \) is the order number, and \( \lambda \) is the wavelength of light. The distance between fringes on the screen can also be related to the geometry of the setup.
02

Identify Known Values

We are given:- Wavelength, \( \lambda = 450 \) nm = \( 450 \times 10^{-9} \) m- Distance between the screen and the slits, \( L = 1.80 \) m- Distance between dark fringes, \( \Delta y = 3.90 \) mm = \( 3.90 \times 10^{-3} \) mThese values will be used in calculations to determine the slit separation.
03

Relate Fringe Spacing to Given Values

For small angles, \( \sin \theta \approx \tan \theta \times \theta \approx \frac{y}{L} \). The distance between two consecutive dark fringes (fringe spacing) is given by:\[ \Delta y = \frac{\lambda L}{d} \]This formula relates the fringe spacing, wavelength, slit separation, and distance between the screen and slits.
04

Solve for Slit Separation

Re-arranging the equation \( \Delta y = \frac{\lambda L}{d} \) for \( d \), we have:\[ d = \frac{\lambda L}{\Delta y} \]Substitute the known values:\[ d = \frac{450 \times 10^{-9} \times 1.80}{3.90 \times 10^{-3}} \]
05

Calculate the Result

Carrying out the calculation:\[ d = \frac{450 \times 10^{-9} \times 1.80}{3.90 \times 10^{-3}} = \frac{810 \times 10^{-9}}{3.90 \times 10^{-3}} \approx 2.08 \times 10^{-4} \text{ m} \]Thus, the slit separation \( d \) is approximately \( 2.08 \times 10^{-4} \) meters.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Wavelength
In the context of the double-slit interference experiment, the wavelength is a key component that describes the distance between consecutive peaks (or troughs) of a wave. Wavelength is usually denoted by the Greek letter \( \lambda \) and is often measured in nanometers (nm) for visible light.

The wavelength in this exercise is 450 nm, equivalent to \( 450 \times 10^{-9} \) meters. This value indicates the color of the light, which in this case, is in the blue spectrum. Different wavelengths will affect how light interferes with itself, changing the pattern of light and dark bands observed on the screen. Shorter wavelengths will typically lead to closer spacing of interference fringes, while longer wavelengths result in wider spacing.

Understanding the wavelength allows us to predict the behavior of light in various interference setups, such as through different slit separations or varying distances to the screen.
Fringe Spacing
Fringe spacing refers to the distance between two consecutive bright or dark fringes on the screen in a double-slit experiment. This distance, often denoted by \( \Delta y \), is determined by the interaction of coherent light waves as they superimpose on one another after passing through the slits.

In this exercise, the fringe spacing is 3.90 mm, or \( 3.90 \times 10^{-3} \) m. It represents how the interference pattern spreads out on the screen. Larger fringe spacing occurs when the interference pattern is spread more widely, which can be the result of varying factors such as the slit separation, the wavelength of the light, or the distance to the screen.
  • Formulas: The relationship between fringe spacing and other factors can be expressed as \( \Delta y = \frac{\lambda L}{d} \). This equation considers the wavelength \( \lambda \), slit separation \( d \), and the screen distance \( L \).
  • Factors Influencing Fringe Spacing: Changes in wavelength or slit separation have a direct impact on \( \Delta y \), altering the interference pattern observed.
Slit Separation
Slit separation, denoted as \( d \), is an essential factor in determining the pattern created in a double-slit experiment. The distance between the two slits affects how the light waves emerge and interfere with each other.

In this exercise, solving for the slit separation involves using the formula \( d = \frac{\lambda L}{\Delta y} \). By substituting the known values of wavelength (450 nm), screen distance (1.80 m), and fringe spacing (3.90 mm), the slit separation is found to be approximately \( 2.08 \times 10^{-4} \) meters.
  • As the slit separation \( d \) decreases, the interference pattern generally becomes more spread out, leading to wider fringe spacing.
  • A larger slit separation causes the fringes to appear closer together on the screen.
  • Understanding and calculating slit separation is crucial for predicting and manipulating the interference pattern of waves.
Screen Distance
The distance from the slits to the screen, denoted as \( L \), is a critical factor in determining the size and distribution of the interference pattern in a double-slit experiment. This parameter influences how the light waves overlap after passing through the slits.

For this problem, the screen distance is given as 1.80 meters. An increase in this distance tends to spread the fringes farther apart, leading to larger fringe spacing. Conversely, decreasing the screen distance would bring the fringes closer together, decreasing fringe spacing.
  • Geometric Relationship: The angle \( \theta \) at which lights interfere is small, so \( \sin \theta \approx \tan \theta \approx \frac{y}{L} \).
  • Impact on Pattern: Changes in the screen distance directly affect the interference spacing, thus influencing which order of fringes might be visible.
Understanding screen distance and its relationship with other factors such as wavelength, fringe spacing, and slit separation helps in designing experiments to observe specific interference patterns.

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Most popular questions from this chapter

Jan first uses a Michelson interferometer with the 606-nm light from a krypton-86 lamp. He displaces the movable mirror away from him, counting 818 fringes moving across a line in his field of view. Then Linda replaces the krypton lamp with filtered 502-nm light from a helium lamp and displaces the movable mirror toward her. She also counts 818 fringes, but they move across the line in her field of view opposite to the direction they moved for Jan. Assume that both Jan and Linda counted to 818 correctly. (a) What distance did each person move the mirror? (b) What is the resultant displacement of the mirror?

A researcher measures the thickness of a layer of benzene (\(n\) = 1.50) floating on water by shining monochromatic light onto the film and varying the wavelength of the light. She finds that light of wavelength 575 nm is reflected most strongly from the film. What does she calculate for the minimum thickness of the film?

Red light with wavelength 700 nm is passed through a two-slit apparatus. At the same time, monochromatic visible light with another wavelength passes through the same apparatus. As a result, most of the pattern that appears on the screen is a mixture of two colors; however, the center of the third bright fringe (\(m\) = 32) of the red light appears pure red, with none of the other color. What are the possible wavelengths of the second type of visible light? Do you need to know the slit spacing to answer this question? Why or why not?

What is the thinnest soap film (excluding the case of zero thickness) that appears black when illuminated with light with wavelength 480 nm? The index of refraction of the film is 1.33, and there is air on both sides of the film.

Coherent light with wavelength 600 nm passes through two very narrow slits and the interference pattern is observed on a screen 3.00 m from the slits. The first-order bright fringe is at 4.84 mm from the center of the central bright fringe. For what wavelength of light will the first-order dark fringe be observed at this same point on the screen?

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