This preview shows pages 1–2. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: ECE344, Midterm Exam 1: Solutions October 19, 2009 1. Problem: The workfunction of a material is defined as the energy required to remove an electron from the material and is usually indicated by the Greek letter (pron: khi). The workfunction of gold is Au = 4 . 9 eV, the workfunction of cesium is Cs = 1 . 9 eV. a. Calculate the maximum wavelength (in nm) of light required to remove an electron from Au via the photoelectric effect. b. Do the same for Cs. Solution: Since = c = 2 hc h = 2 h E , (1) or, expressing the energy in eV: = 2 h eE , (2) using E = Au we have = 253 nm and using E = Cs we get = 653 nm. 2. Problem: Electrons in a swarm at thermal equilibrium have each an average kinetic energy of (3 / 2) k B T . a. Calculate the value of (3 / 2) k B T in eV. b. Calculate the velocity (in cm/s) of an electron having a kinetic energy equal to the average energy (3 / 2) k B T . This is the socalled thermal velocity. c. Calculate its average de Broglie wavevelength in cm. This is called the thermal wavelength....
View
Full
Document
 Spring '10
 Polizinni

Click to edit the document details