Exams › JEE Main › Physics
A sample of copper and a sample of germanium are both cooled from room temperature down to 77 K. What happens to their electrical resistances?
- The resistance of copper rises, while that of germanium falls
- The resistance of both materials falls
- The resistance of both materials rises
- The resistance of copper falls, while that of germanium rises
Correct answer: The resistance of copper falls, while that of germanium rises
Solution
As temperature decreases, the resistance of metals like copper typically decreases due to reduced thermal vibrations of atoms, which allows electrons to flow more freely. In contrast, germanium, a semiconductor, experiences an increase in resistance at low temperatures because fewer charge carriers are available for conduction.
Related JEE Main Physics questions
- For a diode, the current–voltage relation is I = (e^(1000V/T) - 1) mA, where V is the applied voltage in volts and T is the temperature in kelvin. If the current is 5 mA at 300 K and the voltage measurement has an uncertainty of ±0.01 V, what is the resulting error in the current (in mA)?
- A common-emitter amplifier has a current gain of 62. Its collector resistance is 5 kΩ and its input resistance is 500 Ω. If the applied input voltage is 0.01 V, what is the output voltage?
- A half-wave rectifier employing a p-n junction diode is fed with an AC voltage of peak value 25 V and frequency 50 Hz. The circuit has no filter, and the load resistance is 1000 Ω. If the diode’s forward resistance R_f is 10 Ω, what is the rectification efficiency in percent?
- At 27°C, germanium has an intrinsic conductivity of 2.13 mho m−1. If the electron and hole mobilities are 0.38 m2V−1s−1 and 0.18 m2V−1s−1, respectively, what is the charge-carrier concentration?
- A transistor in good condition has its three terminals labeled P, Q, and R. When checked with a multimeter, there is no conduction between P and Q. However, if the negative lead of the meter is connected to R and the positive lead is connected to either P or Q, the meter shows some resistance. What can be concluded about the transistor?
- At 300 K, intrinsic silicon has a hole concentration of 7 × 10¹⁵ m⁻³. If antimony is introduced into silicon at the rate of 1 atom per 10⁷ silicon atoms, and only one-half of the impurity atoms supply electrons to the conduction band, by what factor does the charge-carrier concentration rise because of doping? Take the number of silicon atoms in 1 m³ to be 5 × 10²⁸.
⚔️ Practice JEE Main Physics free + battle 1v1 →