Why does a diffraction grating separate colours

A diffraction grating is a large collection of evenly spaced parallel slits that produces an interference pattern similar to but sharper than that of a double slit. The number of slits in this diffraction grating is too large. Etching in integrated circuits can be done to a resolution of 50 nm, so slit separations of nm are at the limit of what we can do today. This line spacing is too small to produce diffraction of light. Skip to main content. Wave Optics.

Search for:. Multiple Slit Diffraction Learning Objectives By the end of this section, you will be able to: Discuss the pattern obtained from diffraction grating.

Explain diffraction grating effects. Figure 5. Example 1. Calculating Typical Diffraction Grating Effects Diffraction gratings with 10, lines per centimeter are readily available. Find the angles for the first-order diffraction of the shortest and longest wavelengths of visible light and nm. What is the distance between the ends of the rainbow of visible light produced on the screen for first-order interference? See Figure 6. Conceptual Questions What is the advantage of a diffraction grating over a double slit in dispersing light into a spectrum?

What are the advantages of a diffraction grating over a prism in dispersing light for spectral analysis? Can the lines in a diffraction grating be too close together to be useful as a spectroscopic tool for visible light? If so, what type of EM radiation would the grating be suitable for?

If a beam of white light passes through a diffraction grating with vertical lines, the light is dispersed into rainbow colors on the right and left. If a glass prism disperses white light to the right into a rainbow, how does the sequence of colors compare with that produced on the right by a diffraction grating?

Suppose pure-wavelength light falls on a diffraction grating. What happens to the interference pattern if the same light falls on a grating that has more lines per centimeter? What happens to the interference pattern if a longer-wavelength light falls on the same grating? Explain how these two effects are consistent in terms of the relationship of wavelength to the distance between slits. Suppose a feather appears green but has no green pigment. Explain in terms of diffraction.

It is possible that there is no minimum in the interference pattern of a single slit. Explain why. Is the same true of double slits and diffraction gratings? At what angle will the first-order maximum be for nm-wavelength green light? Find the angle for the third-order maximum for nm-wavelength yellow light falling on a diffraction grating having lines per centimeter.

How many lines per centimeter are there on a diffraction grating that gives a first-order maximum for nm blue light at an angle of What is the distance between lines on a diffraction grating that produces a second-order maximum for nm red light at an angle of Calculate the wavelength of light that has its second-order maximum at The distance between them is therefore.

Significance The large distance between the red and violet ends of the rainbow produced from the white light indicates the potential this diffraction grating has as a spectroscopic tool. The more it can spread out the wavelengths greater dispersion , the more detail can be seen in a spectrum. This depends on the quality of the diffraction grating—it must be very precisely made in addition to having closely spaced lines.

Check Your Understanding If the line spacing of a diffraction grating d is not precisely known, we can use a light source with a well-determined wavelength to measure it. Suppose the first-order constructive fringe of the emission line of hydrogen is measured at using a spectrometer with a diffraction grating. What is the line spacing of this grating? Take the same simulation we used for double-slit diffraction and try increasing the number of slits from to.

The primary peaks become sharper, and the secondary peaks become less and less pronounced. By the time you reach the maximum number of , the system is behaving much like a diffraction grating. A diffraction grating has lines per centimeter. At what angle will the first-order maximum be for nm-wavelength green light? Find the angle for the third-order maximum for nm-wavelength yellow light falling on a difraction grating having lines per centimeter. How many lines per centimeter are there on a diffraction grating that gives a first-order maximum for nm blue light at an angle of?

What is the distance between lines on a diffraction grating that produces a second-order maximum for nm red light at an angle of? Calculate the wavelength of light that has its second-order maximum at when falling on a diffraction grating that has lines per centimeter.

An electric current through hydrogen gas produces several distinct wavelengths of visible light. What are the wavelengths of the hydrogen spectrum, if they form first-order maxima at angles and when projected on a diffraction grating having 10, lines per centimeter?

Decreasing the number of lines per centimeter by a factor of x means that the angle for the x -order maximum is the same as the original angle for the first-order maximum. What is the spacing between structures in a feather that acts as a reflection grating, giving that they produce a first-order maximum for nm light at a angle? An opal such as that shown in Figure acts like a reflection grating with rows separated by about If the opal is illuminated normally, a at what angle will red light be seen and b at what angle will blue light be seen?

At what angle does a diffraction grating produce a second-order maximum for light having a first-order maximum at? The analysis shown below also applies to diffraction gratings with lines separated by a distance d. What is the distance between fringes produced by a diffraction grating having lines per centimeter for nm light, if the screen is 1. Gratings with these small separations are obtained by using the regularly arranged rows of closely spaced ions found in the lattice structure of salt crystals.

Like a prism , a diffraction grating separates the colors in white light to produce a spectrum. The spectrum, however, arises not from refraction but from the diffraction of the light transmitted or reflected by the narrow lines in the grating. When light passes through a narrow opening, it is diffracted spread out like water waves passing through a narrow barrier. With a transmission type diffraction grating, light waves are diffracted as they pass through a series of equally spaced narrow openings.

A similar effect takes place if light is reflected from a reflecting grating. The beam formed by the combination of diffracted waves from a number of openings in a transmission grating forms a wave front that travels in the same direction as the original light beam.

This beam is often referred to as the central maximum.