Not all long-distance phone calls are made over phone wires.Today,phone wires are being replaced by fiber optics.Fiber optics make telephoning faster and easier than ever before.
In the past,telephone calls were made mostly over copper wires.Copper wires are heavy and bulky.Fiber optics are flexible,glass fibers.They are no thicker than a human hair.A wire cable is as thick as a mans arm.An optical fiber cable is as thick as a thumb.
Fiber optics transfer sound into light.First,a person speaks into a phone.The sound is changed into electrical impulses.A small laser changes the electrical impulses into coded bursts of light.The light is decoded hack into electrical impulses at the telephone recieving station.Finally,the electrical impulses are changed into sounds again at the receiving telephone.
Optical fibers transimit calls much faster than copper wires can.The laser pulses with light as fast as 90 million times a second.At that speed,every word in a dictionary can be sent through a single fiber in a few seconds.Optical fibers also save space.A few fibers can carry more calls than thousands of strands of copper cable.
Optical fibers will be used for video as well as voice communications.And they will prove useful in computer-to-computer hookups.However,it will take years to replace existing wires.
1.Which of the following best expresses the main point of the passage?
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