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Phantom Bulb


The bulb stays lit even once it is turned off!

concave mirror

For more information about Phantom Bulb. Updated on: 04/22/2015


An effective way to show that a concave mirror produces a real image (of magnification 1) at the centre of curvature for any object positioned at the centre of curvature.


Large concave mirror(a base used to hold the mirror in place goes with the mirror), phantom bulb box, light bulb


The mirror is placed to face the audience and by trial the image of the concealed lamp (wiring concealed) can be made to coincide exactly with the unlit lamp on top of the box so that the unlit lamp appears to be bright.Make sure the gap between the lamp and the mirror is around 20 cm. The unlit lamp can then be removed from its socket for the sake of showmanship. The illusion is satisfactory for observers within a 30' angle directly in front of the mirror.


Demo room information

Location —-
Maker Unknown
Current State Working
demonstrations/6_optics/6a_geometrical_optics/phantom_bulb/start.txt · Last modified: 2019/02/14 23:33 (external edit)