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NEET2026PhysicsChapterActual

A piece of copper and a piece of germanium are cooled from room temperature ( 300 K ) to 80 K . Which of the following statements is correct regarding their electrical resistances?

Options

  1. AThe resistance of both copper and germanium will decrease.
  2. BThe resistance of copper will decrease while that of germanium will increase.
  3. CThe resistance of copper will increase while that of germanium will decrease.
  4. DThe resistance of both copper and germanium will increase.

Correct answer

B. The resistance of copper will decrease while that of germanium will increase.

Step-by-step solution

Copper is a metallic conductor. For metals, the temperature coefficient of resistivity is positive. As temperature decreases, the thermal agitation of atoms decreases, which increases the relaxation time of free electrons. This leads to a decrease in electrical resistance. Germanium is a semiconductor. For semiconductors, the number density of charge carriers (electrons and holes) decreases exponentially with a decrease in temperature ( n e^ -E_g / 2kT ). This reduction in charge carriers leads to an increase in el

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