The U.S. Food and Drug Administration limits the radiationleakage of microwave o

Question

The U.S. Food and Drug Administration limits the radiationleakage of microwave ovens to no more than 5.0 mW/cm2 at a distanceof 2.00 in. A typical cell phone, which also transmits microwaves,has a peak output power of about 2.0 W. (a) Approximating the cell phone as a point source, calculatethe radiation intensity of a cell phone at a distance of 2.00 in.How does the answer compare with the maximum allowable microwaveoven leakage? (Answer as the ratio of cellphone power / microwavepower.) (b) The distance from your ear to your brain is about 2 in.What would the radiation intensity in your brain be if you used aBluetooth headset, keeping the phone in your pocket, 1.0 m awayfrom your brain? Most headsets are so-called Class 2 devices with amaximum output power of 2.5 mW.
I have part A done and cannot figure out how to do partB. The U.S. Food and Drug Administration limits the radiationleakage of microwave ovens to no more than 5.0 mW/cm2 at a distanceof 2.00 in. A typical cell phone, which also transmits microwaves,has a peak output power of about 2.0 W. (a) Approximating the cell phone as a point source, calculatethe radiation intensity of a cell phone at a distance of 2.00 in.How does the answer compare with the maximum allowable microwaveoven leakage? (Answer as the ratio of cellphone power / microwavepower.) (b) The distance from your ear to your brain is about 2 in.What would the radiation intensity in your brain be if you used aBluetooth headset, keeping the phone in your pocket, 1.0 m awayfrom your brain? Most headsets are so-called Class 2 devices with amaximum output power of 2.5 mW.
I have part A done and cannot figure out how to do partB.

Explanation / Answer

a) Formula for the radiation intensity of a cell phone at adistance (d) is                        I = P / (4d2)                           = (2.0W) / [4(2.0in)2]                           = 61.67W/m2                           = 61.67*10-4W/cm2                           = 6.167mW/cm2 Now the ratio of cellphone power / microwave power =(6.167mW/cm2) / (5.0 mW/cm2) = 1.233 Now the ratio of cellphone power / microwave power =(6.167mW/cm2) / (5.0 mW/cm2) = 1.233

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