Thermodynamics >
Heat and the First Law > Radiation
DCS# 4B40.10
LIGHT THE MATCH
APPARATUS
24" diameter parabolic
reflectors
202-06-A
matches
202-02-C3
heater coil and mounted
socket
101-12-D
foamcore
shield
202
DESCRIPTION
The two reflectors are aligned on
a common central axis and placed about three meters apart,
with the heat source at the focal point of one and a match at
the focal point of the other. Turn on the heater and
after about 45 seconds the match will ignite, demonstrating
that infrared radiation propagates and reflects in the same
manner as visible light.
NOTES
The focal length of the
reflectors is 6". The reflectors have center holes
through which the heater coil and match holder can be
supported.
You can judge when the mirrors are aligned and the coil
properly positioned by sighting through the hole in the match
mirror toward the glowing coil and its reflection. Then,
with the match in place, use parallax between the match and
the heater reflection to precisely position it. If
needed, the piece of foam core can be used to find the focal point for the match, and
as a heat shield during setup.
The variac is not necessary for the demonstration but can be
useful when aligning things.
Blackening the match heads and
preheating the cone heater will speed things up a bit.
It takes about 30 seconds for the match to start to smoke and
another 15 seconds or so to light.
