| A measure of how easily a material conducts electricity. It is defined as the product of resistance and cross-sectional area, divided by the length of the material. | Resistivity (ρ) |
| How is resistivity (ρ) calculated? | ρ = RA/L, where R is resistance, A is cross-sectional area, and L is the length of the material. |
| Resistivity allows comparison of materials’ electrical conductance, even if they are not the same size. It represents the resistance of a 1-meter length of a material with a 1 m² cross-sectional area. | Purpose of Resistivity |
| Why is resistivity useful for comparing materials? | It gives the resistance of a standard-sized sample of material (1 meter in length, 1 m² cross-sectional area), making it easier to compare different materials. |
| Resistivity is affected by temperature. For metal conductors, increasing the temperature increases resistivity because atomic vibrations increase, causing more frequent collisions between electrons and atoms. | Temperature Dependence of Resistivity |
| What happens to the resistivity of a metal when its temperature increases? | The resistivity increases because the atoms vibrate more, leading to more collisions with electrons, which decreases the current and increases resistance. |
| When the temperature of a metal conductor increases, the resistance increases. This is due to increased atomic vibrations causing more frequent collisions between charge carriers and atoms. | Effect of Temperature on Resistance |
| Why does resistance increase in a metal conductor when temperature rises? | As temperature rises, atomic vibrations increase, leading to more frequent collisions with electrons, which slows down the electrons, decreasing current and increasing resistance. |
| A type of resistor whose resistance decreases as its temperature increases. | Thermistors |
| What happens to the resistance of a thermistor as its temperature increases? | The resistance decreases because electrons are emitted from atoms, increasing the number of charge carriers, which increases current and decreases resistance. |
| A graph for a thermistor shows that as temperature increases, the resistance decreases. | Temperature-Resistance Graph |
| What is one application of thermistors in circuits? | Thermistors are used as temperature sensors, which can trigger an event when the temperature reaches a certain value, such as turning on heating when the room temperature drops below a set value. |
| A material that, below a certain temperature (called the critical temperature), has zero resistivity. | Superconductor |
| What is the critical temperature of a superconductor? | The temperature below which a superconductor has zero resistivity. It varies by material but is typically very close to 0 K (-273°C). |
| Superconductors can be used in: Power cables, to eliminate energy loss through heating. Strong magnetic fields, which don't require a constant power source, for use in maglev trains and medical applications. | Applications of Superconductors |
| How do superconductors reduce energy loss in power cables? | Since superconductors have zero resistivity, their resistance is also zero, meaning no energy is lost as heat during transmission. |
