Light the Match

WARNING: The filament voltage is potentially lethal. The filament and the focussed beam are extremely hot. Use with extreme caution!

Equipment: A 2 meter optical rail, a wooden match mounted on a rail saddle, two parabolic reflectors mounted on rail saddles, one filament mounted on a rail saddle, one variac and a piece of scrap paper.

What it does: The parabolic reflectors focus the heat from the filament onto the match and the match ignites.

Concepts Demonstrated: Transfer of heat by radiation.

Classroom assembly:

1. Place the optical rail on a bench so that it is perpendicular to the class.
2. Mount one parabolic reflector on each end of the optical rail and orient them so they face each other.
3. Mount the filament in front of the reflector closest to the class.
4. Plug the filament into the variac.
5. Mount the match in front of the reflector farthest from the class.
6. Set the variac to 0V and turn it on.
7. Turn the voltage up to 120V.
8. Using the piece of scrap paper, align the mirrors so they focus the filament onto the match.
9. Remove the paper. The match will ignite.

• Turn the voltage up AFTER you have turned on the variac. If you set the voltage before turning on the variac, you will blow the variac fuse.

WARNING: The filament voltage is potentially lethal. The filament and the focussed beam are extremely hot. Use with extreme caution!

Setup Time: Medium. The alignment is tricky and takes some fiddling. It has to be realigned in the lecture hall before class.

Difficulty: Straightforward.

Visibility: High. The apparatus is large and the ignition of the match is visible from far away. This demonstration is appropriate in a large lecture hall.

Related demonstrations:

References: PIRA 4B40.10

Original Construction: All parts were purchased.