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應用光學 Homework 1 1. The wavefunction of a transverse wave on a string is ( x, t ) (30.0cm) cos[(6.28rad / m) x (20.0rad / s)t ]. Compute the (a) frequency, (b) wavelength, (c) period, (d) amplitude, (e) phase velocity, and (f) direction of motion. 2. Draw the wavefront of the following uniform plane waves: (a) ( x, t ) cos(x t ) (b) (r , t ) cos(x y t ) 3. An electromagnetic wave in a dielectric medium is specified by the following function: 1 E (r , t ) (6iˆ 3 5 ˆj )(10 4 V / m) exp{i[ ( 5 x 2 y ) 10 7 9.42 1015 t ]} 3 Find (a) the direction along which the electric field oscillates, (b) the amplitude E0 of 4. E , (c) propagation number and wavelength, (d) the speed. A light bulb puts out 20W of radiant energy (most of it IR). Assume it to be a point source and calculate the irradiance of 1.00m away.