Partial preview of the text
Download PHYS 2102 Problem set 7 and more Exercises Physics in PDF only on Docsity!
40. ee INT The electron beam inside an old television picture tube is 0.40 mm in diameter and carries a current of 50 vA. This electron beam impinges on the inside of the picture tube screen. a. How many electrons strike the screen each second? b. What is the current density in the electron beam? c. The electrons move with a velocity of 4.0 x 10’ m/s. What electric field strength is needed to accelerate electrons from rest to this velocity in a distance of 5.0 mm? d. Each electron transfers its kinetic energy to the picture tube screen upon impact. What is the power delivered to the screen by the electron beam? 44, ee INT Ina classic model of the hydrogen atom, the electron moves around the proton in a circular orbit of radius 0.053 nm. a. What is the electron’s orbital frequency? b. What is the effective current of the electron? 49. ee The resistivity of a metal increases slightly with increased temperature. This can be expressed as p = po[1 + a(T — Tp)], where To is a reference temperature, usually 20°C, and a is the temperature coefficient of resistivity. For copper, a = 3.9 x 10-> °C-!. Suppose a long, thin copper wire has a resistance of 0.25 Q at 20°C. At what temperature, in °C, will its resistance be 0.30 Q? 63. °° What diameter should the nichrome wire in Figure P27.63 be in order for the electric field strength to be the same in both wires? Figure P27.63 62. 24. © The two wires in Figure P27.62© are made of the same material. What are the current and the electron drift speed in the 2.0-mm-diameter segment of the wire? Figure P27.62 = 20% 10 mAs rege) 1.0 mm 2.0mm * The two segments of the wire in Figure EX27.24'5 have equal diameters but different conductivities o; and 0). Current I passes through this wire. If the conductivities have the ratio o)/o, = 2, what is the ratio E2/E; of the electric field strengths in the two segments of the wire? Figure EX27.24 
