Answers for the Teacher Only

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What Do You Think?

The scanner works by reflecting a laser beam from the bar code. Since the long and short bars reflect different amounts of light, the photodetector and its electronics can identify the bar pattern from the reflected light. This pattern is converted to a digital code. In a modern scanner, the bar code can be five or ten centimeters from the scanner and need not be in a particular location. To scan in a range of directions, the laser beam is reflected from a spinning hologram, which pulls the beam back and forth hundreds of times per second. The bar code itself works by coding for the digits from zero to nine, according to the code shown on page 292.