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Which of the following statements about a Light Emitting Diode (LED) are correct? (I) It operates at low voltage and consumes little power. (II) It responds instantly with no warm-up time needed. (III) The bandwidth of emitted light is roughly 100 to 500 angstroms, making it nearly (but not perfectly) monochromatic. (IV) It has a short operational life but is mechanically rugged. (V) It can switch on and off very rapidly.

1. I, II, III, IV are correct
2. I, III, IV, V are correct
3. I, II, III, V are correct
4. All five statements are correct

Correct answer: I, II, III, V are correct

Solution

LEDs do operate at low voltage (I), respond instantly with no warm-up (II), emit nearly monochromatic light in a 100-500 angstrom band (III), and can switch on/off rapidly (V). However, LEDs are famous for their very long life, so statement IV (which claims short life) is incorrect. The correct combination is I, II, III, V.

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