======LED Photocell======


<WRAP right box>
**Materials: **{{$demo.materials_description}}\\
**Difficulty: **{{$demo.difficulty_description}}\\
**Safety: **{{$demo.safety_description}}\\
\\
**Categories:** {{$demo.categories}}
\\


**Alternative titles:** LED Photoelectric Effect Demonstration  
</WRAP>

====Summary====                   
{{$demo.summary}}



====Procedure====  
  - Insert a clear green LED into a piece of card and mount it in a clamp stand.  
  - Connect the LED to a high-resistance voltmeter using crocodile clips.  
  - Shield the LED from ambient light using a black tube or darkened room until the voltmeter reads zero.  
  - Shine a white torch directly at the LED and observe the small voltage produced.  
  - Repeat with a red laser pointer and note no measurable voltage.  
  - Repeat with a green laser pointer and observe a non-zero voltage again.



====Links==== 
📄 LED photocell - Institute of Physics: [[https://spark.iop.org/led-photocell]]\\


====Variations====
  * Try LEDs of different colors to see how each responds to different photon energies.  
  * Use multiple light sources of varying frequency (blue, yellow) for comparison.  
  * Collect quantitative data of voltage produced vs. wavelength to plot a threshold graph.



====Safety Precautions====
  * Use only class 2 lasers from reputable suppliers.  
  * Clamp lasers securely and direct beams away from eyes.  
  * Conduct the activity in a controlled, darkened environment to reduce stray light.  
  * Avoid touching LED leads directly while in circuit to prevent inaccurate readings.




====Questions to Consider====
  * Why does the red laser not produce a reading, even though it is brighter than the torch? (Because red photons have lower frequency and therefore less energy.)  
  * What determines whether photons can release electrons in the LED? (Their frequency/energy, not their intensity.)  
  * How does this experiment demonstrate light behaving as a particle? (Each photon delivers a packet of energy, and only sufficiently energetic photons release electrons.)  
  * How is this related to the photoelectric effect studied by Einstein? (Both show a threshold frequency below which no electrons are emitted, regardless of light intensity.)