This animation identifies the multiples of 3 and 5 to identify the least common multiple of the two. A teacher could use this animation to verify student understanding and provide a visual example of LCM. Additional examples and explanations would improve this tutorial.
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LED ReQuiz Answer KEY
Part I: Concepts & Content
Aluminum or Gallium
Contributed by N-type dopant atoms
Red LED has the longest wavelength
Increasing the bandgap of the LED
Part II: Problem Solving
(a) Frequency is 6.92e14 Hz which corresponds with blue light. (b) 4.59e-19 J which is the same as 2.86 eV. (c) Silicon Carbide, or SiC.
(a) Holes are positive and abundant in the P-type semiconductor; Electrons are negative and abundant in the N-type semiconductor. (b) Electricity will flow from the negative pole of the power source to the positive pole. (c) Since the LED is composed of Gallium Arsenide, with a bandgap energy of 1.43 eV, the light will be red/infrared with a frequency of 3.45e14 Hz.
Part III: Critical Thinking
(a) Ground state electrons in hydrogen must gain a minimum quanta of energy to become excited to a higher energy level (greater than n=1). Once excited, these electrons will emit energy in the form of light when they fall back to the ground state. (b) A transition of 3 to 2 is more likely to result in visible light, as visible light is generally low in energy and the 2 to 1 transition is much higher in energy than the 3 to 2 transition.
In answering how a LED works, students should indicate the following:
Electrons flow from negative to positive
Energy is absorbed by electrons and then some of it is later released as light
Electrons move through a circuit and combine with holes within the semiconductor
The color emitted is related to the energy bandgap
The energy bandgap is determined by the semiconductor material