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Chapt_26

# Chapt_26 - University Physics(Prof David Flory Chapt_26...

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University Physics (Prof. David Flory) Chapt_26 Sunday, February 03, 2008 Page 1 Name: __________________________ Date: _____________ 1. The current density is the same in two wires. Wire A has twice the free-electron concentration of wire B. The magnitude of the average velocity of electrons in A is: A) twice that of electrons in B B) four times that of electrons in B C) half that of electrons in B D) one-fourth that of electrons in B E) the same as that of electrons in B 2. Copper contains 8.4 × 10 28 free electrons/m 3 . A copper wire of cross-sectional area 7.4 × 10 –7 m 2 carries a current of 1 A. The magnitude of the average electron velocity is approximately: A) 3 × 10 8 m/s B) 10 3 m/s C) 1 m/s D) 10 –4 m/s E) 10 –23 m/s 3. For an ohmic resistor, resistance is the proportionality constant for: 4. A certain wire has resistance R . Another wire, of the same material, has half the length and half the diameter of the first wire. The resistance of the second wire is: A) R /4 B) R /2 C) R D) 2 R E) 4 R Write the letter for the correct answer on the answer sheet. Write clearly.

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