11 - EM Waves

# 11 - EM Waves - Physics 8B 11 EM Waves rev 4.0 11 EM Waves...

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Physics 8B 11 – EM Waves rev 4.0 1 11 – EM Waves 1. Shown below are mathematical and pictorial representations of an electromagnetic plane wave propagating through empty space. The electric field is parallel to the z- axis; the magnetic field is parallel to the y-axis. Note: x ˆ , y ˆ , and z ˆ are unit vectors along the +x, +y, and +z directions, respectively. E(x, y, z, t) = E 0 sin(kx + ! t) z ˆ B(x, y, z, t) = B 0 sin(kx + ! t) y ˆ y 4 B 3 x 1 z E •2 a) In which direction is the wave propagating? Explain. b) Is the wave transverse or longitudinal? Explain. c) Points 1, 2 and 3 lie in the x-z plane and point 4 lies in the x-y plane. For the instant shown, rank these points according to the magnitude of the electric field. d) Is your ranking consistent with the mathematical expression for the electric field? Explain. e) For the instant shown, rank points 1, 2, 3 and 4, according to the magnitude of the magnetic field. f) Is your ranking consistent with the mathematical expression for the magnetic field? Explain. Physics 8B 11 – EM Waves rev 4.0 2 2. A simple periodic wave of electromagnetic radiation is moving in the direction shown below. P, Q, R, S and T are equally spaced points in the path of the wave. The distance PQ = d, the velocity of the wave is c, and its wavelength is 4d. An observer at T, looking towards P, would see H and D as vertically upwards, while E, A and B 1 would be horizontal and to their left. At a given instant, the magnetic field at P is a maximum, and is represented by the vector B 1 . D H P C Q R G B 1 S

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## This note was uploaded on 09/18/2011 for the course PHYSICS 8B taught by Professor Shapiro during the Fall '07 term at Berkeley.

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11 - EM Waves - Physics 8B 11 EM Waves rev 4.0 11 EM Waves...

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