【正文】 is is and it of the yaxis is. So . The real value of the Planck constant is, so the result is not very accurate. There exist some errors. First of all, as the weakness of the LEDs and eyes cannot tell the fringes center accurately, the distance (y) from fringes to the center fringe is not accurate and it will lead to the inaccuracy of frequency. Secondly, the voltage used should be the instant voltage while the LED was just starting to shine. However, this is impossible to achieve. The above two errors are the largest causes of errors. The distance (L) between the grating to the center fringe is also not accurate as it read by eyes, which is the third error. Therefore, errors on reading the distance and the voltage are two approximate measurement errors (10). In addition, the uncertain errors also exist. The LED may shine abnormally as it was used before or some other internal problems are in the LED, this may is an error and it is uncertain..Operating this experiment in the dark, using the new LEDs and using other materials which are more stable instead of carton are three measurements can be done to improve the accuracy of this experiment (10). The answers from the LED with two colors cannot be used to find as it is not monochromatic light and it has two frequencies (11). The error in the method for finding h can be calculated by this method which is, where is the corrected standard deviation. .The Planck constant, Four colors of light were measured, so . From table 7, , are , , and respectively. So . Substituting them and can be worked out which is. Therefore,(12).according to the website which is called Investopedia (2012), the standard deviation stands for the rate of deviation between the stochastic variable and the mathematic expectation, so a low means that the result s were close together. The standard deviation of the result gotten from aim 4 is from the real h. as the errors of the results have no regular pattern, the errors are random, not systematic(12).ConclusionThis lab has finished 4 aims which are building a spectrometer, finding wavelengths for lasers and LEDS and finding the Planck constant, the Planck constant was also gotten from the experiment based on the light diffraction and the photoelectric effect. To sum up, the spectrometer used to measure wavelengths is useful as it can produces the diffraction pattern and shows the pattern on the screen. Also, the distance from the fringes to the center fringe can be read from the bottom’s ruler directly as well as the distance from the center fringe to the grating. The spectrometer is easy to be made and operated. However, due to the unstable property, the data must be read from the viewing hole and the light will lose from it, the spectrometer is not very accurate. From Wikipedia, there is another way to measure the Planck constant which is Watt balance method. The Watt balance is a tool to pare two powers, one of which is measured in conventional electrical units and the other is in SI watts. According to the explanation of the conventional watt, with SI unit can be measured where is the Von Klitzing constant and it can be measured from the effect of quantum Hall. In the particular situation can be assumed, thus, the Planck constant can be measured directly from the formula (13). Compared with the photoelectric effect, the watt balance method to measure the Planck constant is hard to be operated and it only can work in the particular situation, in addition, the result gotten from this method also not very accurate. Therefore, the photoelectric effect is better and easier than the watt balance method to measure the Planck constant. Reference:Investopedia (2012) Standard deviation [Internet], Available from: [Accessed 15th May 2012].Wikipedia (2012) Watt balance [Internet], Available from: [Accessed 15th May 2012].17English Name: Vince Class: Eng11B Chinese Name: Wen Zheng Yang Student number: SBC11102