A sample of copper and a sample of germanium are chilled from room temperature down to 77 K.
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Answer: C. The resistance of copper decreases and that of germanium increases.
Explanation
Cooling a metal (copper) decreases its resistance, while cooling a semiconductor (germanium) increases its resistance. Metals have positive temperature coefficients, meaning resistance drops as thermal vibrations decrease. Semiconductors have negative temperature coefficients, causing fewer charge carriers to be thermally excited at low temperatures. Copper is a standard metallic conductor widely used in electrical wiring applications. Germanium is a metalloid semiconductor used in early transistor and diode electronics. Temperature drastically alters the electrical conductivity properties of different material classes.
Superconductors exhibit zero resistance at extremely low temperatures, unlike ordinary copper. Semiconductor behavior at cryogenic temperatures is vital for designing specialized electronic sensors. Physics experiments frequently demonstrate these contrasting thermal responses of conductors and semiconductors. Option A claims both increase, which ignores the metallic conductivity decrease upon cooling. Option B states both decrease, failing to account for semiconductor freeze-out effects. Option D reverses the behaviors by incorrectly stating copper resistance increases.
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