# Current and Resistance

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 Author: tigerlilyy ID: 302223 Filename: Current and Resistance Updated: 2015-05-06 06:37:08 Tags: fizik Folders: Description: Fizik II. Vize Show Answers:
1. An electric current in a conductor
2. The SI unit of electric current
Ampere (1A=1C/s)
3. The total charge that passes through the plane in time interval 0-t
4. Charge of an electron
1 e- = 1.6 x 10-19 C
5. Direction of current
• Current and positive charge carriers move in the same direction
• Actual charge carriers are negative and move in the opposite direction.

higher potential(+)lower potential (-)
6. AC - DC
Alternating Current: Provided by power companies

Direct Current: Provided by batteries
7. Current Density
Vector quantity. Flow of charge through the cross-section of conductor at particular point.

•  (dot product)
•
•  (A/m2)
8. Direction of current density
Positive moving charges→Same with their velocity

Negative moving charges→Opposite of their velocity
9. Drift speed of the charge carriers
When an electric field E is established in a conductor, the charge carriers (assumed positive) acquire a drift speed vd in the direction of E.

(ne=carrier charge density)

10. The resistance of a conductor
11. Resistivity of a conductor

• (σ is the conductivity of the material)
• (E is the magnitude of of the applied electric field)
12. The applied electric field
13. The resistance R of a conducting wire
14. Change of ρ with temperature
15. Ohm's Law in a macroscopic view or Resistivity of a metal

• n: number of free electrons per unit volume
• : mean time between the collisions of an electron with the atoms of the metal
16. Power
17. Resistive Dissipation
If the device is a resistor, we can write:
•
• In a resistor, electric potential energy is converted to internal thermal energy
18. Semiconductors
The materials that have a few coduction electrons but can become conductor when they are doped with other atoms that contribute free electrons.
19. Superconductors
The materials that lose all electrical resistance at low temperatures.