advertisement

Problem 1 A laser pointer delivers 0.10 mW average power in a beam 0.90 mm in diameter. Find (a) the average intensity, (b) the peak electric field, (c) the peak magnetic field. Solution: SP 1 2 d 157 W/m2. 4 E0 2 0 c S 2S 0 / 0 2S /( 0 c) 344 V/m B0 E0 c 1.15 T . Problem 2 At 1.5 km from the transmitter, the peak electric field of a radio wave is 350 mV/m. (a) What is the transmitter’s power output, assuming it broadcasts uniformly in all directions? (b) What is the peak electric field 10 km from the transmitter? Solution: 2 2 (a) P 4 r (E 0 2 0c) 4.59 kW 2 2 ' (b) Since r E 0 const , E 0 (r r')E 0 52.5 mV/m at a distance of 10 km. Problem 3 13 of a particular TV station’s signal is 1.0 10 W/m2 when it The average intensity arrives at 33-cm –diameter satellite TV antenna. (a) Calculate a total energy received by the antenna during 6 hours of viewing this station’s programs. (b) What are the amplitudes of E and B fields of the EM wave? Solution: This is Problem 53 in Giancoli textbook. 1 (a) E St d 2 1.8 10 10 J . 4 (b) E0 2 0 c S 2S 0 / 0 2S /( 0 c) 8.7 10 6 V / m. B0 E0 / c 2.9 10 14 T .