C cell phones: physical

c cell phones: physical

Mona Chiang

The camera cell phone tops many teens’ wish lists. That’s because it’s handy and discreet for snapping and transmitting images to the Internet or other cell phones. Unfortunately, this gadget is generating worldwide concerns of privacy loss. Camera phones have caused outcries from unsuspecting people who found their images–many intrusive–posted on the Web.

To make a snapshot, the phone houses a tiny digital camera. Instead of film, a digital camera uses a computer chip called a Charged Coupled Device (CCD). A matrix sits on the CCD. “It’s like a chess-board with many rows and columns of tiny dots,” explains Saswato Das of Bell Laboratories. On each dot, or pixel, is a photosensitive (light-sensitive) element. When the lens zeros in on, say, your dog, the pixels react to light bouncing off “Spot” by generating an electrical signal. “Basically, each pixel records one part of the object, and each dot generates a different intensity of charge,” says Das. “But everything adds up to form a picture.” To send the image, the bundles of electrical charges are converted into a digital signal, or a series of on-off pulses. The information is then transmitted via radio waves. (See step 1, left)

To stop sneaky shutterbugs, many health clubs have banned cell phones from their changing rooms. The South Korean government’s tactic: New-model phones must emit a signal when a picture is snapped.

Do you think camera cell phones should be banned in some public places? If so, why?


Digital cell phones are small two-way radios. When you speak into the phone, sound waves cause a disk inside the phone’s microphone to vibrate. Electrical components “read” the disk’s vibrations and turn words into an electrical signal. A microchip then converts the electrical signal into a digital signal–a series of on-off pulses. Then …


The cell phone’s antenna transmits the digital signal via radio waves–invisible light waves–that move through the air. Cell phones use a specific range of radio frequencies. (Frequency measures the number of waves per second.)


The radio waves travel to a base station, or radio tower, which serves one geographical region called a cell. Each radio tower is “tuned in” to the frequencies cell phones use, so it “hears” calls as they come in.


The base station forwards the signal to the closest switching office, where powerful computers route calls. The area code tells computers where to direct the call. If it’s going to a wired phone, the switching office sends the call to the local phone network over phone lines. If the call is going to another cell phone, the switching office forwards the call to another base station or to a satellite via radio waves.


Communications satellites in low orbit around Earth serve as a “constellation” of base stations and switching offices in the sky. The satellites pass calls to other satellites, to ground stations, or directly to high-powered cell phones.


The satellite passes the call back to a switching office on Earth. Computers locate the receiving cell phone by sending out a signal to each cell using a specific frequency. When the phone picks up the signal, it rings.

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