planck constant albert hong st. mark’s school. why led? syllabus –hkale –hkdse – atomic...
Post on 24-Dec-2015
214 Views
Preview:
TRANSCRIPT
Why LED?
• Syllabus– HKALE– HKDSE – Atomic World
• Let student familiar with the connection of the circuit – a taste of electronics
• Cheap– $0.5/LED– With $200 for setting up 10 set for assessment
Forward Bias
• Current starts to flow when the potential difference is large enough to overcome the barrier created by the electric field.
• When electrons cross the boundary and move into holes, they move from higher-energy states to lower-energy ones. Photons emit.
Experiment (2)
• By changing the voltage supply, different currents can be obtained
• y-intercept the graph equals to hc/q
• By giving students , h can be obtained
Experiment (3)
• The experiment can continue by giving students LED of unknown wavelengths
• Using h found to find unknown • Blue, green or even IR
Assessment
• Graph plotting technique – suitable scale
• Extract information from unfamiliar situation – no such experiment in most of the AL textbooks.
• 10 groups can be easily setup – TAS can be done in the same session
Extension
• Can integrate with the experiment of finding wavelength with diffraction grating
• Use the found to obtain h
• Investigation – different ways to find emitted by LED? Diffraction grating, circuit, etc.
Points to note
• Red LED’s spectrum is narrower – Better if you are using the LED in diffraction grating experiment
• Start measurement from Vin = 8-10V
LED Current /mA Vs Voltage /v
y = 24.723x - 42.855 y = 18.383x - 48.329y = 26.839x - 50.129
y = 14.881x - 39.413
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
1.0 1.3 1.5 1.8 2.0 2.3 2.5 2.8 3.0 3.3
Input Voltage /v
Cur
rent
/ m
A
V Blue led / v
V Red led / v
V Green led / v
V Yellow led / v
Other resources
• About dark matter• Simple enough for students with basic
knowledge of gravitation and circular motion• Video with worksheets for students• http://
www.perimeterinstitute.ca/index.php?option=com_content&task=view&id=691&Itemid=657
top related