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6) Magnetic resonance imaging, or MRI, and positron emission tomography, or PET scanning, are two medical diagnostic techniques. Both employ electromagnetic waves. For these waves, find the ratio of the MRI wavelength (frequency = 6.64 x 10' Hz) to the PET scanning wavelength (frequency = 1.23 1020 Hz). 7) Two astronauts are 1.3 m apart in their spaceship. One speaks to the other. The conversation is transmitted to earth via electromagnetic waves. The time it takes for sound waves to travel at 343 m/s through the air between the astronauts equals the time it takes for the electromagnetic waves to travel to the earth. How far away from the earth is the spaceship? m 8) A laser emits a narrow beam of light. The radius of the beam is 1.20 x 10 m, and the power is 1.50 x 10 W. What is the intensity of the laser beam? W/m2 9) An industrial laser is used to burn a hole through a piece of metal. The average intensity of the light is S = 1.22 10° W/m2. What is the rms value of each of the following fields in the electromagnetic wave emitted by the laser? (a) the electric field N/C (b) the magnetic field T