Physics Fundamentals ( Phys1001 ) - 1760 Words

Lab Report Module Name: Physics Fundamentals (PHYS1001) Experiment Name: Determination of Planck’s constant (h) Student P-number: P14177341 Lab Tutor : Dr Shashi Paul Date: 14/11/2014 Abstract The objective was to determine the value of Planck’s constant using LED’s. The value of Planck’s constant found in this experiment was 5.93x10-34Js, This is fairy close in comparison to the accepted value being 6.626x10-34Js. The Value of Planck’s constant was found with the use of LED’s, the provided wavelength was used to calculate the frequency, then the experiment allowed us to find the LED’s Turn on voltage. The findings were plotted to a graph where, start up voltage was on the Y axis and†¦show more content†¦the electrons crossing the junction are excited and return to their stable state, usually the ground state. When returning to the ground state or a lower state from which they were in, the electron emits light energy which is a high energy photon. The energy of the photon depends on how many energy states the electron drops. This particular voltage when the LED just starts to emit light is known as the threshold voltage. Once the threshold voltage is reached the current may increase but the voltage across the LED doesn t change significantly. The energy of the photon emitted can be calculated using the equation E = hf where h = the Planck’s constant f = the frequency of light From the equation it can be said that the energy emitted has a relationship with planck’s constant and the frequency of emitted radiation. We can use this equation to work out planck’s constant by combining it with another equation. This equation is E = QV where Q = the charge (1.6x10-19) V = threshold voltage hf=QV If you plot a graph of voltage against frequency, find the gradient and multiply it by the charge of an electron (1.6x10-19), you find the value of Planck’s constant. Experiment / Materials and Methods Apparatus: Circuit board LED’s blue to infrared Resistor in series on circuit board 100ÃŽ © Smartphone camera Procedure: Firstly set up apparatus, then connect the diodes one at a