LECT9_176182

# LECT9_176182 - Temperature coefficient of resistivity e=...

This preview shows pages 1–8. Sign up to view the full content.

Temperature coefficient of resistivity )] T T ( 1 [ o o α + ρ = ρ )] T T ( 1 [ R R o o α + = ρ T 0 = reference temperature α = temperature coefficient of resistivity, units of (ºC) -1 For Ag, Cu, Au, Al, W, Fe, Pt, Pb: values of α are ~ 3-5 × 10 -3 (ºC) -1 T slope = α

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Typical tungsten filament: ~1 m long, but 0.05mm in radius. Calculate typical R. A = π (5x10 -5 m) 2 = 7.9x10 -9 m 2 ρ = 5.6x10 -8 Ω m (Table 17.1) R = ρ L/A = (5.6x10 -8 Ω m) (1m)/ 7.9x10 -9 m 2 = 7.1 Ω Note: As per section 17.6, the resistivity value used above is valid only at a temperature of 20°C, so this derived value of R holds only for T=20°C. Please note -- I edited some values here compared to the slide I presented in lecture!
Calculate ρ at T=4000°C, assuming a linear ρ -T relation: For tungsten, α = 4.5x10 -3 /°C ρ = ρ 0 [1+ α (T-T 0 )] = 8.3x10 -7 Ω m R = ρ L/A = 106 Ω . (note-- this is still less than the estimate of >200 Ω we’ll derive in class in a few minutes… I suspect the ρ -T relation in reality may not be strictly linear over such a wide range of temperature; my guess would be that the above value of α may only be valid for temperatures of tens to hundreds of °C)

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Superconductors For some materials, as temperature drops, resistance suddenly plummets to 0 below some T c . Once a current is set up, it can persist without any applied voltage because R 0!
Superconductors Applications: •Energy storage at power plants •Superconducting magnets with much stronger magnetic fields than normal electromagnets •Super conducting distribution power lines could eliminate resistive losses

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
More recently: As the field has advanced, materials with higher values of T c get discovered
Electrical Energy and Power

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern