Subject: Physics   / General Physics
Question
PHYS320_W7_iLab9O_Datasheet
DATA SHEET
Name: __________________ Date: ___________
10 questions @ 3 points each. 30 points total.
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Data
1. Record the wavelength and voltage offsets from the measurement on each LED in the table below. Use the measured wavelengths from Week 3 Lab #4 to complete the wavelength column. (3 points)
2. Calculate a value for Planck’s constant for each measurement and find an average. (3 points)
color
wavelength l (nm)
Y offset (V)
h (´10-34 J×s)
red
624
1.63
5.42
orange
620
1.70
6.52
amber
607
yellow
591
2.1
6.62
yellow green
575
1.85
green
525
1.9
5.32
blue
470
2.48
6.22
super purple
400
2.85
average
3. Compare the average of your measurements with the accepted value.gif”> and calculate a percent difference. (3 points)
The percent difference is ________
4. Paste a copy of your capacitor voltage versus time graph with fits here. (3 points)
Questions
5. Explain why a LED’s brightness is proportional to the electric current flowing through it. (3 points)
6. The current passing through a LED experiences a voltage drop. Use conservation of energy to explain why this voltage drop must occur. (3 points)
7. A photon of blue light has more energy than a photon of red light. Why must a LED that produces blue photons have a larger voltage drop than a LED that produces red photons? (3 points)
8. How does the resistor in the circuit protect the LED? (3 points)
9. A LED’s color is determined by the energy needed to shift an electron across the band gap in the semiconductor from which the LED is made. Because blue photons have more energy than green photons, the development of blue LEDs has been slow. The materials needed to produce blue LEDs are almost true insulators rather than semiconductors. What distinguishes a semiconductor from an insulator? (3 points)
10.What would be the wavelength of a photon emitted by a standard silicon diode (Eg@ 0.7 eV)? Where in the electromagnetic spectrum is this wavelength? (3 points)
