Name: Harry W.
How is it possible to measure the wavelength of light
emitted from an Infra Red heating element?
The wavelength(s) of infrared radiation is measured with an instrument
called an infrared spectrometer [or spectrophotometer]. It consists of a
slit of variable width which forms an slit-image of the impinging infrared
radiation. The infrared image is then focused by mirrors on to a grating [in
older instruments this element could be a large crystal of NaCl] designed to
diffract infrared radiation, that is spatially separate the radiation
according to wavelength in much the same way a prism spatially separates the
various wavelengths of visible light. The diffracted infrared radiation then
passes through a second slit that shields the detector from all the
diffracted radiation except a narrow bandwidth. This narrow bandwidth of
radiation falls on an infrared detector. The infrared detector can be any
number of devices that convert the radiation impinging upon it to an
electrical signal that is amplified and displayed on some sort of chart. The
detector can be a thermocouple, or any number of solid state devices.
I hope that is not more about "elephants" than you cared to know!
Radios are sensors constructed to detect specific wavelengths much longer
than infrared light. Televisions respond to specific wavelengths between
radio and infrared. Digital cameras respond to wavelengths in the visible
range. Just adjust the sensors so they notice slightly longer wavelengths
and you have a camera with sensors that respond to infrared. By having the
frequency/wavelength adjustment like a radio tuner, you can determine the
wavelength by "tuning in" to the signal from the heating element.
Click here to return to the Physics Archives
Update: June 2012