Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538
Physics Demo Manual
Demonstrations are cataloged according to PIRA Bibliography
PLEASE REQUEST DEMOS WELL IN ADVANCE
Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.
Choose a subtopic:
(Clicking a green button will add that demo to your list)
- Geometrical Optics
- The Eye
video - Light The Match
To show that parallel rays of light entering a parabolic mirror are focused on the focal point and vice-versa.
DEMO VIDEO DOWNLOAD / no audio / 1920x1080 / 24.19Mb/s / 331MB size
DEMO VIDEO DOWNLOAD / no audio / 854x480 / 5.69Mb/s / 75MB size
Place the lamp at the focus of the source mirror and insert a match (with the end colored black with a Sharpie) in the holder attached to the target mirror. When the light is turned on, the match will flame up (typically within 10 to 30 seconds).
Lining up both mirrors is straightforward:
In general, use the reflection in the mirror itself. To make sure the match head is lined up properly, look beyond the match head at the reflection in the mirror. The match head should be centered in the image of the opposing reflector. Use the same method for lining up the projector bulb in the other mirror.
- make sure match tip is marked black with a Sharpie pen so IR radiation is more efficiently absorbed
- set 1000 Watt projector bulb 10.5cm from center of source mirror
- set match holder 40cm from center of target mirror
- turn on 1000 Watt projector bulb and move source mirror from side to side until it looks roughly aimed to the center of the target mirror
- using a white sheet of paper, look at the light focus spot at the match holder
- move target mirror from side to side and/or up and down until the focus spot on the paper lines up with the tip of the match in holder
- fine adjusting the focus by moving the 1000 Watt projector bulb back and forward at the source mirror can increase the speed at which the match will burst into flames
- Large Concave Mirrors