Temperature coefficient of resistance in a pure semiconductor is
Negative
Pure Semiconductor Temperature Coefficient Explained
The temperature coefficient of resistance quantifies how the electrical resistance of a material changes with temperature. For a material, it's often represented by the symbol $\alpha$. It indicates the fractional change in resistance per degree Celsius (or Kelvin) change in temperature.
Pure semiconductors, such as intrinsic silicon or germanium, exhibit a distinct behavior concerning their electrical resistance when subjected to temperature variations.
Semiconductor Behavior with Temperature
- Charge Carrier Generation: In pure semiconductors, electrical conduction relies on charge carriers (electrons and holes). At absolute zero temperature, a pure semiconductor acts as an insulator because all valence electrons are bound in covalent bonds.
- Thermal Excitation: As the temperature increases, thermal energy becomes available. This energy allows some valence electrons to break free from their covalent bonds, becoming mobile electrons in the conduction band. Simultaneously, the absence of an electron in the bond creates a hole in the valence band, which can also move and contribute to conduction.
- Increased Conductivity: The number of free electrons and holes (charge carriers) increases exponentially with temperature. More charge carriers mean that the material can conduct electricity more easily.
- Resistance Change: Since conductivity is inversely proportional to resistivity (and hence resistance), an increase in the number of charge carriers leads to higher conductivity and consequently, lower resistance. The increase in carrier concentration with temperature is the dominant factor in determining the resistance change.
This phenomenon, where the resistance of a material decreases as its temperature increases, is known as having a Negative Temperature Coefficient of Resistance (NTC).
In contrast, metals typically have a Positive Temperature Coefficient of Resistance because increased temperature leads to greater lattice vibrations, which scatter the electrons and impede their flow, thus increasing resistance.
The size of the specimen does not determine the fundamental nature (positive or negative) of the temperature coefficient of resistance, which is an intrinsic property of the material itself.
Important Questions from Miscellaneous
A stone is thrown horizontally from the top of a 20 m high building with a speed of 12 m/s. It hits the ground at a distance R from the building. Taking g = 10 m/s2 and neglecting air resistance will give :
A sphere of volume V is made of a material with lower density than water. While on Earth, it floats on water with its volume f1V (f1 < 1) submerged. On the other hand, on a spaceship accelerating with acceleration a < g (g is the acceleration due to gravity on Earth) in outer space, its submerged volume in water is f2V. Then:
A railway wagon (open at the top) of mass M1 is moving with speed v1 along a straight track. As a result of rain, after some time it gets partially filled with water so that the mass of the wagon becomes M2 and speed becomes v2. Taking the rain to be falling vertically and the water stationery inside the wagon, the relation between the two speeds v1 and v2 is :
Consider the following statements:
1. Distance between the longitudes becomes zero on North Pole and South Pole.
2. Distance between the longitudes is maximum on the Equator.
3. Number of longitudes is more than number of latitudes.
Which of the statements given above is/are correct?
One block of 2⋅0 kg mass is placed on top of another block of 3⋅0 kg mass. The coefficient of static friction between the two blocks is 0⋅2. The bottom block is pulled with a horizontal force F such that both the blocks move together without slipping. Taking acceleration due to gravity as 10 m/s2, the maximum value of the frictional force is :
