Spectral lines

Electricity and Magnetism Level 3

A light beam is split by a prism into its spectral colors, so that the spectrum shown below results. What is the light source of this beam?

Fluorescent light bulb Laser LED Daylight Incandescent light bulb

1 solution

Markus Michelmann
Dec 11, 2017

Daylight: The spectrum of the sun is similar to that of a blackbody radiator. Even though absorption and scattering change the light spectrum, daylight has a largely continuous spectrum with only a few gaps.
Incandescent light bulb: In a conventional light bulb, light is generated by heating a thin wire by electric current. The spectrum is therefore also a continuous blackbody spectrum as in the sun, even though the bulb's color temperature is much lower.
Fluorescent light bulb: In a fluorescent tube is thin mercury gas, which is excited by electric discharge to glow and emits radiation in the UV range. By coating the glass tube with a phosphor, this UV radiation is converted by fluorescence into visible light. The spectrum of the fluorescent tube is thus composed of the atomic spectral lines of the mercury and the phosphor. These correspond to individual discrete wavelengths of light.
LED: A light-emitting diode consists of a semiconductor having a band gap between valence and conduction band. When a current flows through the LED, recombination of charge carriers occurs, emitting a photon whose frequency is approximately equal to the energy gap. The light spectrum of the LED therefore has almost only one color. To produce white light, therefore, different colored LEDs must be combined.
Laser: A laser is based on the principle of light amplification by stimulated emission. An atom can be induced to emit a photon when it is stimulated by photons of the same wavelength. The fact that the emitted photons stimulate further atoms to emit similar photons results in a kind of chain reaction. The spectrum of a laser ideally contains only monocromatic light of a single wavelength.

Spectral lines

1 solution

0 pending reports