School of Physics Lecture Demonstration Manual

Na-8 Band Gap Energy

Published: Friday 17 March 2006 - Updated: Thursday 31 March 2011


To demonstrate the bang gap energy of a pn junction.



Click on pictures to enlarge.

Band Gap Pic


A red LED is illuminated with a desk lamp. The photons have enough energy for the electrons to overcome the energy gap in the pn junction and a current is displayed on the galvanometer. If the same desk lamp illuminates a blue LED the photons do not have enough energy to produce a current flow. However if the leds are illuminated with a UV source a current will now flow.

Safety notes

Electrical safety 


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