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 ata distance of 2.00 in. A typical cell phone, which also transmitsmicrowaves, has a peak output power of about 2.0 W. (a) Approximating the cell phone as a pointsource, calculate the radiation intensity of a cell phone at adistance of 2.00 in. How does the answer compare with the maximumallowable microwave oven leakage? (Answer as the ratio of cellphonepower / microwave power.)

(b) The distance from your ear to your brain is about 2 in. Whatwould 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.
The U.S. Food and Drug Administration limits the radiationleakage of microwave ovens to no more than 5.0 mW/cm2 ata distance of 2.00 in. A typical cell phone, which also transmitsmicrowaves, has a peak output power of about 2.0 W. (a) Approximating the cell phone as a pointsource, calculate the radiation intensity of a cell phone at adistance of 2.00 in. How does the answer compare with the maximumallowable microwave oven leakage? (Answer as the ratio of cellphonepower / microwave power.)

(b) The distance from your ear to your brain is about 2 in. Whatwould 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.
(a) Approximating the cell phone as a pointsource, calculate the radiation intensity of a cell phone at adistance of 2.00 in. How does the answer compare with the maximumallowable microwave oven leakage? (Answer as the ratio of cellphonepower / microwave power.)

(b) The distance from your ear to your brain is about 2 in. Whatwould 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.

Explanation / Answer

a Icell = P / A= P /(4d2)=2.0W/[4(2.0in)2]= 61.7 W/m2= 61.7*10-4 W/cm2= 6.17mW/cm2 =>(6.17 mW/cm2) / (5.0 mW/cm2) =1.233 b Distance (d) between the pocket to the brain = 1.0m I = P / 4d2 = (2.5mW) /[4(1.0m)2]

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