18 Questions
What term represents the resistivity of a metal at 0°C?
ρ0C
How does an increase in temperature affect the resistivity of a metal?
Increases it
What does the residual component of electrical resistivity in a metal result from?
Presence of impurity atoms
How does close proximity of atoms influence electron energy bands in a solid material?
Splits each atomic state into electron energy bands
Which factor becomes significant only at low temperatures in determining the total resistivity of a metal?
Residual component
What happens to the vibration amplitude of positive-ion cores as the temperature of a metal increases?
Increases
What mainly determines the conductivity of a material?
Energy band structure
In a semiconductor, where does an electron transition to when enough energy is supplied?
Conduction band
What type of material has conductivities between good conductors and insulators?
Semiconductors
How does the resistivity of a semiconductor change with increasing temperature?
Decreases
What can valence electrons in a semiconductor become under certain conditions?
Free electrons
What determines the specific properties of a semiconductor?
Impurities added to it
What is the material constant that relates quantities such as resistance, length, and cross-sectional area in a conductor?
Electrical resistivity
At room temperature, which type of material exhibits the highest electrical conductivity?
Pure metals
What range of values characterizes the conductivity of insulators at room temperature?
10-10 to 10^-20 (Ω.m)^-1
What is the relationship between resistivity and temperature in materials?
Resistivity increases with temperature.
What is the electrical conductivity range of semiconductors at room temperature?
10-6 to 10^4 (Ω.m)^-1
What component of resistivity accounts for the increase in resistivity when temperature rises?
Thermal resistivity component
Study Notes
Electrical Resistivity
- Electrical resistivity (ρ) is a material constant that depends on temperature.
- The units for electrical resistivity are ohm-meters (Ω.m).
- ρT = ρ0C(1+ αTT) where ρ0C is resistivity at 0°C, αT is the coefficient of resistivity, and T is the temperature of the metal.
Factors Affecting Resistivity
- As the temperature of a metal increases, the vibration of the positive-ion cores increases, causing the release of photons that scatter conduction electrons and increase resistivity.
- Resistivity also increases due to structural imperfections like dislocations, grain boundaries, and impurity atoms.
Energy Band Structure in Solids
- When atoms come close together, electrons are perturbed by adjacent atoms, resulting in a series of closely spaced electron states termed an electron energy band.
- Each atomic state splits into a band consisting of multiple states.
Conductivity
- Conductivity depends on two factors: atomic bond and energy band structure.
- Metals have high conductivity due to strong ionic bonds and a small energy gap between the valence and conduction bands.
- Semiconductors have low conductivity due to weaker covalent bonds and a larger energy gap.
- Insulators have very low conductivity due to strong covalent bonds and a large energy gap.
Semiconductors
- Semiconductors are materials with conductivity between good conductors and insulators.
- The resistivity of a semiconductor decreases as temperature increases.
- Semiconductor properties depend on the impurities or dopants added to the material.
- At higher temperatures, semiconductors act like conductors, and at lower temperatures, they act like insulators.
Ohm's Law
- Electrical conductivity (σ) is a measure of the ability of a material to conduct electricity.
- The units for electrical conductivity are (ohm-meter)^-1 or (Ω.m)^-1.
- Ohm's Law relates electrical conductivity, resistivity, and the passage of electric current.
Electrical Conductivity of Materials
- Pure metals like silver, copper, and gold have the highest conductivities (about 10^7 (Ω.m)^-1).
- Electrical insulators like polyethylene and polystyrene have very low conductivities (about 10^-14 (Ω.m)^-1).
- Semiconductors like silicon and germanium have conductivities in between (about 10^-6 to 10^4 (Ω.m)^-1).
Test your knowledge on electrical resistivity, which is a material constant related to resistance based on the length and cross-sectional area of a conductor. Explore the concept of electrical conductivity as an alternative to resistance in understanding electric current flow.
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