2. [8/20 Points] DETAILS PREVIOUS ANSWERS SERCP9 21.P.050. | MY NOTE (a) The distance to a star is approximately 4.90 x 1018 m. If this star were to burn out today, in how many years would we see it disappear? 5.17e2 \\J/ years (b) How long does it take for sunlight to reach Mars? 13 x Your response is within 10% of the correct value. This may be due to roundoff error, or you could have a mistake in your calculation. Carry ou minimize roundoff error. minutes (c) How long does it take for a microwave radar signal to travel from Earth to the Moon and back? _w (d) How long does it take for a radio wave to travel once around the Earth in a qreat circle, close to the planet's surface? 5. [13.34/20 Points] PREVIOUS ANSWERS SERCP9 21.P.076. ASK YOUR TEACHER The U.S. Food and Drug Administration limits the radiation leakage of microwave ovens to no more than 5.0 mW/cm2 at a distance of 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, calculate the radiation intensity of a cell phone at a distance of 2.00 in. mwxcmz How does the answer compare with the maximum allowable microwave oven leakage? (Enter the ratio of cellphone intensity to microwave intensity.) [microwave (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 a Bluetooth headset, keeping the phone in your pocket, 1.0 m away from your brain? Most headsets are so-called Class 2 devices with a maximum output power of 2.5 mw. (Include both the radiation from the phone and the headset.) 0.024 y mW/cmz