Question

Which of the following has negative temperature coefficient of resistance? (A) \(\mathrm{Fe}\) (B) \(\mathrm{C}\) (C) \(\mathrm{Mn}\) (D) Ag

Short answer

Carbon (\(\mathrm{C}\)) has a negative temperature coefficient of resistance, meaning its resistance decreases as the temperature increases. Therefore, the correct answer is (B) Carbon.

Step-by-step solution

Option A: Iron (\(\mathrm{Fe}\))

Iron has a positive temperature coefficient of resistance, meaning that the resistance increases as the temperature increases. Therefore, Iron is not the correct answer.

Option B: Carbon (\(\mathrm{C}\))

Carbon is unique among the choices here because it has a negative temperature coefficient of resistance. As the temperature increases, its resistance decreases. Therefore, Carbon is the correct answer.

Option C: Manganese (\(\mathrm{Mn}\))

Manganese has a positive temperature coefficient of resistance, meaning that the resistance increases as the temperature increases. Therefore, Manganese is not the correct answer.

Option D: Silver (\(\mathrm{Ag}\))

Silver has a positive temperature coefficient of resistance, meaning that the resistance increases as the temperature increases. Therefore, Silver is not the correct answer. After evaluating each option, we can conclude that: Carbon (B) has a negative temperature coefficient of resistance and is the correct answer.

Key concepts

Negative Temperature Coefficient

Some materials have what is called a "negative temperature coefficient of resistance." This is a property where the resistance of the material decreases as the temperature increases. Carbon, for instance, demonstrates this trait. When you heat carbon, its resistance drops. This behavior is unusual because many conductive materials, like metals, tend to show an increase in resistance when heated. This property can be very valuable in certain applications, such as in thermistors used for temperature sensing.
Here are a few key points about materials with a negative temperature coefficient:

• Resistance decreases with an increase in temperature.
• Common in semiconductors and some alloys.
• Useful in applications where resistance changes can be used for thermal management or sensors.

Materials Resistance

Resistance is an intrinsic property of materials that opposes the flow of electric current. Every material has a distinct resistance, which depends on its atomic structure. For materials like iron, manganese, and silver, their resistance increases as the temperature rises, which means they have a positive temperature coefficient. Understanding a material's resistance is crucial for electrical circuit design and applications.
Different factors influence a material's resistance:

• Type of Material: Conductors have low resistance, while insulators have high resistance.
• Temperature: For most metals, resistance increases with temperature. However, for materials with a negative temperature coefficient, resistance decreases with temperature.
• Dimensions: Longer wires have higher resistance, and thicker wires have lower resistance.

Electrical Conductivity

Electrical conductivity is a measure of a material's ability to conduct electric current. It is the inverse of resistance: materials with high conductivity have low resistance. Metals like silver, iron, and manganese are typically high conductors because their electrons can move freely, allowing electricity to pass through easily.
Conductivity depends on several factors:

• Material Composition: Metals are generally good conductors; non-metals are often not.
• Temperature: Higher temperatures usually decrease conductivity in metals but increase it in materials with a negative temperature coefficient, like carbon.
• Crystalline Structure: The orderly pattern of atoms in a metal helps in the efficient movement of electrons.

Understanding conductivity is essential when selecting materials for electrical applications, ensuring efficient energy transfer and safety.