6A20.60 Lighting a Match

Concepts

Concave mirrors, focal point, reflection, infrared radiation

Overview

High-intensity infrared light ignites a match. The infrared light is generated by a heating coil, collimated by a concave mirror, and then focussed on the match by another concave mirror.

Details

Equipment

  • [2] Concave mirror
  • [2] Lab stand
  • [1] Heating coil
  • [1] Variac
  • [3] Spare fuse
  • [1] Optical rail
  • [1] Match holder
  • [1] Match
  • [2] Saddle
  • [1] Plastic ruler
  • [1] Piece of paper
  • [1] Extension cord
  • [1] Fire extinguisher

Classroom Assembly

  1. Choose one side of the room for demo setup. Place the optical rail there.
  2. Mount the coil and match holder in saddles and secure them to opposite ends of the optical rail. The match holder should be placed so that it's visible to most of the audience.
  3. Place the mirrors on either side of the optical rail.
  4. Carefully align the mirrors to each other.
  5. Place a match in the match holder. The match and coil should each be about 9.5 cm from the centre of the closest mirror.
  6. Make sure the variac is at 0 V and off. Plug the coil into the variac and the variac into a power outlet.
  7. Remove the match and quickly run the experiment with a piece of paper at the match-side focus. It should brown and possibly catch fire in a few seconds. If not, re-align the mirrors and try again.
  8. Set the variac to 0 V and turn it off.
  9. Place the match back in the holder.

Important Notes

  • This demo is a significant fire and heat hazard. Do not run this experiment near anything highly flammable. Refresh yourself with the fire extinguisher controls, if necessary.
  • If set up properly, the mirrors should not block anyone's view of the match.
  • Do not run the heating coil for more than 5 minutes at a time. The power cord can get very hot.
  • When running, the coil is a bare, electrically live wire. Beware.

Script

  1. Turn on the variac and, with moderate speed, turn it up to 60 V.
  2. Wait for the coil to redden a bit, then turn the variac to 120 V with moderate speed.
  3. The match should start to smoke in a second and ignite within 10 seconds.
  4. Blow out the match.
  5. Turn down the variac to 0 V and turn it off.

 

Additional Resources

References

  • PIRA 4B40.10, 6A20.60

Disclaimer

  • Don't attempt this at home!

Last revised

  • 2020

Technicals

  • The focal length of the mirrors is about 9.5 cm.

Related AV

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If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.