In this experiment, the Plank's constant would be determined by applying the theoretical wavelength number from the light spectrum and also the experimental voltage data from the measurement. In this experiment, two different colors of light, which had different value for its wavelengh, would be used to calculate the Plank's constant. The first color of light used in this experiment was blus, which had 590 nm for its wavelength, the other color of light used was yellow, which had 450 nm as its wavelengh. One resistor was also used in this experiment, which the experimental voltage would be obtained by measuring the voltage across the resistor. The LED acted like the valve which allows the current to go through, with a minimum amount of provided voltage. With the obtained voltages, the data would be plotted and the slope would be determined. The slope in this graph would represent the product of cf (speed of light times the frequency) with 1/E as the x-axis and λ as the y-axis. With this slope, the Plank's constant could be obtained. On the other hand, the other Plank's constant would be calculated with the equation of photon's energy. These two final results for Plank's constant would then be compared.
Obtain the drop voltage across the LED by knowing the supplied voltage and measuring the voltage across the resistor
Blue-light LED
Yellow-light LED
Data:
|
Color
of light
| <><>
Voltage
(V=eV)
| <><>
Wavelength
λ (nm)
| <><>
|
Blue
| <><>
2.76
| <><>
590
| <><>
|
Yellow
| <><>
1.95
| <><>
450
| <><>
Calculations:
Blue
Energy 2.76×1.602×10-19= 4.42×10-191/E=1/4.42×10-19= 2.26×1018
Yellow
Energy1.95×1.602×10-19= 3.12×10-19
1/E=1/4.42×10-19= 3.20×1018
Final Results:
|
Color
of light
| <><>
Energy
(J)
| <><>
Plank’s
Constant
| <><>
|
Blue
| <><>
4.42×10-19
| <><>
8.70×10-34
| <><>
|
Yellow
| <><>
3.12×10-19
| <><>
4.69×10-34
| <><>
Plank's Constant from the slope:
The value of slope obtined from the measured data is 1.49×10-25
since slope= c times the Plank's constatn, the Plank's constant would be obtined by dividing the slope by the speed of light.
1.49×10-25/3×108=5.0×10-34
The theoretical value for Plank's Constant is 6.63×10-34
Percent Error:
|5.0×10-34-6.63×10-34|/6.63×10-34×100% =
24.58 %
Conclusion:
Based on the Percent Error, it results in a huge difference when the experimental result was compared to the theoretical value. Hence, the Plank's constant did not be correctly determined even the final value was still not too away. From the result data, yellow LED gave us a huge difference on the Plank's constant.
