Experiment XIX: Diffraction-Grating Spectroscopy

Vocabulary flashcards covering key instruments, equations, and theoretical concepts for Experiment XIX: Diffraction-Grating Spectroscopy.

Collimator

A spectrometer component consisting of a slit and a convex lens with the slit in its focal plane that converts light diverging from a source into parallel rays.

Diffraction Grating

A piece of glass with a very large number of ruled lines that separates light into its component colors through interference.

Telescope

A spectrometer component used to observe the image of the slit after light from the source has passed through the diffraction grating.

Grating Spacing ($a$)

The distance between adjacent ruled lines on a diffraction grating, given by the inverse of the number of lines per unit length ($a = \frac{1}{n}$).

Order Number ($m$)

An integer value ($m = 0, 1, 2, \dots$) in the grating formula $a \sin(\theta) = m \lambda$ representing the order of constructive interference.

Goniometer

A built-in device on the spectrometer used to measure the angular position of each emission line viewed through the telescope.

Reticle

A set of cross-hairs intersecting in the center of the field-of-view that permits precise alignment of the telescope with an emission line.

Central Angle ($\theta_0$)

The angular position of the direct beam or zeroth-order image ($m = 0$), used to calculate relative angular displacements of higher-order lines.

Diffraction Pattern Formula

The formula $a \sin(\theta) = m \lambda$ describing constructive interference through multiple slits, where $a$ is grating spacing, $\theta$ is the angle from the normal, $m$ is the order number, and $\lambda$ is the wavelength.

Vernier Scale

A scale on the goniometer that enables determination of angular measurements to an accuracy of $0.1^\circ$.

Prism

A wedge of glass that refracts white light and disperses it into its component colors.

Angular Displacement

The absolute value of the angular separation between the absolute angular position of an emission line and the central angle ($\theta_0$).

Sodium Yellow Lines

Two closely spaced yellow emission lines emitted by a Sodium source with wavelengths $\lambda_1 = 589.0\,nm$ and $\lambda_2 = 589.6\,nm$.