This preview shows pages 1–4. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: Physics 1112 Spring 2009 University of Georgia Instructor: HBSchuttler Solutions toConceptual Practice Problems PHYS 1112 InClass Exam #2A+2B Thu. Apr. 9, 2009, 11:00am12:15pm and 2:00pm3:15pm CP 3.01: If a wire of some length L and a circular crosssection of diameter D has a resistance of 36 k, what will be the resistance of a wire made from the same material, at the same temperature, of length 3 L and the same diameter D ? (A) 4 k (B) 12 k (C) 24 k (D) 72 k (E) 108 k Answer: (E) Using R = L/A and A = ( D/ 2) 2 , we get R L/D 2 . So, R L for fixed D . Increasing L L = 3 L thus increases R R = 3 R = 3 36 = 108. CP 3.02: If a wire of some length L and a circular crosssection of diameter D has a resistance of 36 k, what will be the resistance of a wire made from the same material, at the same temperature, of the same length L and diameter 3 D ? (A) 4 k (B) 12 k (C) 24 k (D) 72 k (E) 108 k Answer: (A) Using R = L/A and A = ( D/ 2) 2 , we get R L/D 2 . So, R 1 /D 2 for fixed L . Increasing D D = 3 D thus changes R R = R/ 3 2 = 36 / 9 = 4. CP 3.03: If a wire of some length L and a circular crosssection of diameter D has a resistance of 36 k, what will be the resistance of a wire made from the same material, at the same temperature, of length 18 L and diameter 3 D ? (A) 4 k (B) 12 k (C) 24 k 1 Physics 1112 Spring 2009 University of Georgia Instructor: HBSchuttler (D) 72 k (E) 108 k Answer: (D) Using R = L/A and A = ( D/ 2) 2 , we get R L/D 2 . Increasing L L = 18 L and D D = 3 D thus changes R R = 18 R/ 3 2 = (18 / 9) 36 = 72. CP 3.04: Three different circuits, X , Y and Z , are built with the same three resistors, R 1 > 0, R 2 > 0, and R 3 > 0, and the same battery of battery voltage E , as shown in Fig. 3.04. Compare and rank the magnitude of the currents I 1 through R 1 , observed in the three different circuits. Fig. 3.04 (X) R 1 I 2 R 3 R 2 I 3 I 1 E R 3 I 2 R 2 R 1 I 1 I 3 E I 3 R 3 R 1 I 1 R 2 I 2 E (Z) (Y) I o I o I o (A) Ranking cannot be determined from information given. (B) I 1 ( X ) > I 1 ( Z ) > I 1 ( Y ) (C) I 1 ( Y ) > I 1 ( X ) > I 1 ( Z ) (D) I 1 ( Y ) > I 1 ( Z ) > I 1 ( X ) (E) I 1 ( Z ) > I 1 ( Y ) > I 1 ( X ) Answer: (D) In circuit Y : R 1 is directly connected to battery, hence I 1 ( Y ) = E /R 1 . In circuit Z : R 1 and R 2 in series are connected to battery. Hence I 1 ( Z ) = E / ( R 1 + R 2 ) < I 1 ( Y ), since R 1 + R 2 > R 1 . 2 Physics 1112 Spring 2009 University of Georgia Instructor: HBSchuttler In circuit X : R 1 , R 2 and R 3 in series are connected to battery. Hence I 1 ( X ) = E / ( R 1 + R 2 + R 3 ) < I 1 ( Z ) < I 1 ( Y ), since R 1 + R 2 + R 3 > R 1 + R 2 ....
View
Full
Document
 Spring '08
 SEATON
 Physics

Click to edit the document details