Question

{"given":"We need to identify which statement about optical fiber telecommunication is NOT true. Optical fibers are transparent glass or plastic fibers that transmit light signals for communication purposes.","key_observation":"Optical fibers transmit information using light waves (electromagnetic radiation in the optical spectrum). A key advantage of optical communication over electrical communication is immunity to electromagnetic interference. Light signals in optical fibers are not affected by external electromagnetic fields, radio waves, or electrical interference.","option_analysis":[{"label":"(A)","text":"Optical fibers can be of graded refractive index.","verdict":"correct","explanation":"This is true. Graded-index optical fibers have a core with refractive index that varies gradually from the center to the edge. This design reduces modal dispersion and improves signal quality."},{"label":"(B)","text":"Optical fibers are subject to electromagnetic interference from outside.","verdict":"incorrect","explanation":"This statement is FALSE. Optical fibers are immune to electromagnetic interference (EMI) from external sources. Since they use light signals instead of electrical signals, they are not affected by radio waves, electrical fields, or other electromagnetic disturbances."},{"label":"(C)","text":"Optical fibers have extremely low transmission loss.","verdict":"correct","explanation":"This is true. Modern optical fibers have very low attenuation, typically around 0.2 dB/km for single-mode fibers at 1550 nm wavelength. This allows long-distance transmission without frequent signal amplification."},{"label":"(D)","text":"Optical fibers may have homogeneous core with a suitable cladding.","verdict":"correct","explanation":"This is true. Step-index optical fibers have a homogeneous (uniform refractive index) core surrounded by cladding with lower refractive index. This creates total internal reflection for light propagation."}],"answer":"(B)","formula_steps":[]}