Changes in the spectral intensity distribution of a hot tungsten filament are observed as the temperature is varied.

How It Works

A slide projector (Beseler Slide King II) with a 1kW lamp and adjustable lens is plugged into a Variac. The light from the projector passes through an inline prism (same as used in Continuous Spectrum) and is projected onto a portable screen. As the Variac increases current to the incandescent projector lamp the intensity of the entire spectrum increases, with the peak intesnsity shifting to the blue end as current increases.

Setting It Up

For best results darken the room as much as possible. Remember to use a slide with a thin vertical slit.

Comments

A good qualitative demonstration to show how the wavelength of the brightest color varies inversely with the temperature of the incandescent lamp. For a more quantitative analysis a spectrometer probe connected to Logger Pro can be used to plot the intensity vs wavelength curve for the projected light.