A lamp filament is made of tungsten. Why do we get a continuous spectrum rather than a tungsten line spectrum when light from an incandescent lamp is viewed with a spectroscope?

When light from an incandescent lamp is viewed with a spectroscope, we observe a continuous spectrum rather than a tungsten line spectrum due to the nature of incandescent light generation.

Incandescent lamps produce light through a process called incandescence. In this process, the lamp filament is heated to a high temperature using an electric current, typically made of tungsten due to its high melting point. As the filament heats up, it emits light.

The reason we observe a continuous spectrum rather than a line spectrum is that incandescent lamps produce light through thermal radiation. When the filament is heated, its atoms vibrate and emit electromagnetic radiation across a wide range of frequencies or wavelengths.

This emission of radiation follows a distribution known as blackbody radiation, which is characterized by a continuous spectrum. The distribution of emitted light intensity at each wavelength depends on the temperature of the filament and is described by the Planck's law.

The temperature of a typical incandescent lamp filament can be around 2700 Kelvin, which corresponds to the warm white light emitted by these lamps. At this temperature, the filament emits light across a broad range of colors, resulting in a continuous spectrum.

In contrast, line spectra are observed when atoms or molecules in a gas or plasma emit light. These line spectra consist of discrete lines of specific wavelengths corresponding to the energies of electronic transitions within the atoms or molecules.

To obtain a line spectrum from tungsten, we would need to excite the atoms in the tungsten gas or plasma, such as by passing an electric current through it, and then observe the light emitted specifically from the excited tungsten atoms. This is different from the process in incandescent lamps, which rely on thermal radiation from the heated filament.

The tungsten filament emits white light, or the entire spectrum of colors of light. (look at any light bulb when its on). When the light is viewed with a spectroscope, it separates the white light into the different colors.