1 / 9

Resistivity Definition Whiteboards

Resistivity Definition Whiteboards. What determines the resistance of a piece of wire?. Resistivity: consider a piece of wire:. R = ρ L A. ρ - Resistivity in Ω m. Some values of ρ in Ω m at 20 o C (From table 18-1 on p 535) Silver 1.59E-8 Copper 1.68E-8 Gold 2.44E-8

pepin
Télécharger la présentation

Resistivity Definition Whiteboards

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Resistivity • Definition • Whiteboards

  2. What determines the resistance of a piece of wire?

  3. Resistivity:consider a piece of wire: • R = ρL • A ρ - Resistivity in Ωm Some values of ρ in Ωm at 20oC(From table 18-1 on p 535) Silver 1.59E-8 Copper 1.68E-8 Gold 2.44E-8 Aluminium 2.65E-8 Tungsten 5.6 E-8 Iron 9.71E-8 Platinum 10.6E-8 Nichrome 100E-8 (alloy of Ni, Fe, Cr) A L • L - Length of the wire in m • A - Cross sectional area of the wire (πr2) • R - Resistance of the wire in Ohms Demo: Different wires

  4. Resistivity: Some values of ρ in Ωm at 20oC (From table 18-1 on p 535) Silver 1.59E-8 Copper 1.68E-8 Gold 2.44E-8 Aluminium 2.65E-8 Tungsten 5.6 E-8 Iron 9.71E-8 Platinum 10.6E-8 Nichrome 100E-8 (alloy of Ni, Fe, Cr) • R = ρL • A Ex #1: A steel wire is 2.7 m long, and has a resistance of 7.3 ohms. What is its diameter? (0.21 mm) • L - Length of the wire in m • ρ - Resistivity in Ωm • A - Cross sectional area of the wire (πr2) • R - Resistance of the wire in Ohms

  5. Whiteboards 1 | 2 | 3

  6. A copper wire is 1610 m long (1 mile) and has a cross sectional area of 4.5 x 10-6 m2. What is its resistance? (This wire is about 2.4 mm in dia) • R = ρL • A • and • A = πr2 • R = ?? • ρ = 1.68E-8 Ωm • L = 1610 m • A = 4.5E-6 m2 • R = 6.010666667 = 6.0 Ω Silver 1.59E-8 Copper 1.68E-8 Gold 2.44E-8 Aluminium 2.65E-8 Tungsten 5.6 E-8 Iron 9.71E-8 Platinum 10.6E-8 Nichrome 100E-8 W 6.0 Ω

  7. An Aluminium wire is 3.2 mm in diameter, and has a resistance of 142 ohms. What length is it? • R = ρL • A • and • A = πr2 • R = 142 Ω • ρ = 2.65E-8 Ωm • L = ?? • A = π(1.6E-3)2 • L = 43095.53817 = 43,000 m Silver 1.59E-8 Copper 1.68E-8 Gold 2.44E-8 Aluminium 2.65E-8 Tungsten 5.6 E-8 Iron 9.71E-8 Platinum 10.6E-8 Nichrome 100E-8 W 43,000 m

  8. A piece of wire has a diameter of 0.42 mm, and a length of 53 cm. What is its resistivity if it has a resistance of 4.9 ohms? (what kind of wire is it?) • R = ρL • A • and • A = πr2 • R = 4.9 Ω • ρ = ?? • L = 0.53 m • A = π(0.21E-3)2 • ρ = 1.28088E-06 = 130x10-8Ωm Silver 1.59E-8 Copper 1.68E-8 Gold 2.44E-8 Aluminium 2.65E-8 Tungsten 5.6 E-8 Iron 9.71E-8 Platinum 10.6E-8 Nichrome 100E-8 W 130x10-8Ωm

  9. Resistivity: Thermal effects. Some values of ρ in Ωm at 20oC(From table 18-1 on p 535) Silver 1.59E-8 Copper 1.68E-8 Gold 2.44E-8 Aluminium 2.65E-8 Tungsten 5.6 E-8 Iron 9.71E-8 Platinum 10.6E-8 Nichrome 100E-8 (alloy of Ni, Fe, Cr) • R = ρL • A ρ – Resistivity will increase with temperature. (random motion, electrons) (demo)

More Related