key term - Positive Temperature Coefficient

Definition

A positive temperature coefficient refers to a property of materials, particularly conductors and semiconductors, where the resistance of the material increases as the temperature rises. This behavior is significant because it helps to explain how materials respond to changes in temperature, affecting their electrical conductivity and overall performance in various applications.

5 Must Know Facts For Your Next Test

1. In metals, the positive temperature coefficient is typically due to increased lattice vibrations as temperature rises, which causes more collisions with charge carriers, resulting in higher resistance.
2. In semiconductors, the positive temperature coefficient indicates that as temperature increases, more charge carriers (electrons and holes) become available for conduction, leading to increased conductivity despite an overall increase in resistance.
3. The positive temperature coefficient is crucial for designing devices such as thermistors, which are used for temperature sensing and control.
4. Not all materials exhibit a positive temperature coefficient; some materials may have a negative temperature coefficient where resistance decreases with increasing temperature.
5. The understanding of positive temperature coefficients is vital in applications like power electronics, where overheating can affect the performance and safety of electronic components.

Review Questions

• How does the positive temperature coefficient affect the resistance of metals as temperature changes?
  • As the temperature of metals increases, their resistance rises due to the increased vibrations of atoms in the lattice structure. These vibrations create more collisions between free-moving electrons and the atomic lattice, which impedes the flow of electrical current. This behavior exemplifies the concept of a positive temperature coefficient, where resistance is directly related to temperature increases.
• Discuss how semiconductors demonstrate a unique response to temperature changes compared to metals regarding their positive temperature coefficient.
  • In semiconductors, the positive temperature coefficient manifests differently than in metals. While increasing temperature raises resistance in metals due to atomic vibrations, semiconductors experience an increase in charge carriers at higher temperatures. This results in increased conductivity, even as resistance may also rise. This unique response allows semiconductors to be engineered for specific applications like transistors and diodes.
• Evaluate the implications of using materials with a positive temperature coefficient in electronic devices, considering both advantages and potential drawbacks.
  • Using materials with a positive temperature coefficient in electronic devices presents several implications. On one hand, these materials can provide enhanced thermal stability and help prevent overheating by limiting current flow at elevated temperatures. However, they can also lead to reduced efficiency in power delivery and potential failures if not properly managed. Engineers must carefully consider these factors when designing circuits to ensure reliability while leveraging the beneficial properties of these materials.

Related terms

Resistance:

Resistance is the opposition that a substance offers to the flow of electric current, measured in ohms (Ω).

Conductivity:

Conductivity is a measure of a material's ability to conduct electric current, often influenced by temperature and material properties.

Semiconductors: Semiconductors are materials that have electrical conductivity between that of insulators and conductors, and their conductivity is highly sensitive to temperature changes.