Practice Midterm 02-solutions

Practice Midterm 02-solutions - sanne (as42476) Practice...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

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

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: sanne (as42476) Practice Exam 02 Yao (59110) 1 This print-out should have 19 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points A 1-megabit computer memory chip contains many 76 fF capacitors. Each capacitor has a plate area of 8 . 6 10 12 m 2 . The characteristic atomic diameter is 10 10 m = 1 A. The permittivity of a vac- uum is 8 . 85419 10 12 C 2 / N m 2 . Determine the plate separation of such a capacitor (assume a parallel-plate configura- tion). Correct answer: 10 . 0192 A. Explanation: Let : A = 8 . 6 10 12 m 2 , C = 76 fF = 7 . 6 10 14 F , and = 8 . 85419 10 12 C 2 / N m 2 . d = A C = ( 8 . 85419 10 12 C 2 / N m 2 ) 7 . 6 10 14 F ( 8 . 6 10 12 m 2 ) = 1 . 00192 10 9 m = 10 . 0192 A . 002 (part 1 of 4) 10.0 points Four capacitors are connected as shown in the figure. 2 2 . 1 F 59 . 3 F 38 . 7 F 8 4 F 98 . 8 V a b c d Find the capacitance between points a and b of the entire capacitor network. Correct answer: 129 . 517 F. Explanation: Let : C 1 = 22 . 1 F , C 2 = 38 . 7 F , C 3 = 59 . 3 F , C 4 = 84 F , and E = 98 . 8 V . C 1 C 3 C 2 C 4 E a b c d A good rule of thumb is to eliminate junc- tions connected by zero capacitance. C 2 C 3 C 1 C 4 a b The definition of capacitance is C Q V . The series connection of C 2 and C 3 gives the equivalent capacitance C 23 = 1 1 C 2 + 1 C 3 = C 2 C 3 C 2 + C 3 = (38 . 7 F) (59 . 3 F) 38 . 7 F + 59 . 3 F = 23 . 4174 F . The total capacitance C ab between a and b can be obtained by calculating the capacitance in sanne (as42476) Practice Exam 02 Yao (59110) 2 the parallel combination of the capacitors C 1 , C 4 , and C 23 ; i.e. , C ab = C 1 + C 4 + C 23 = 22 . 1 F + 84 F + 23 . 4174 F = 129 . 517 F . 003 (part 2 of 4) 10.0 points What is the charge on the 38 . 7 F centered- upper capacitor? Correct answer: 2313 . 64 C. Explanation: The voltages across C 2 and C 3 , respectively, (the voltage between a and b ) are V ab = V 23 = 98 . 8 V , and we have Q 23 = Q 3 = Q 2 = V ab C 23 = (98 . 8 V)(23 . 4174 F) = 2313 . 64 C . 004 (part 3 of 4) 10.0 points A dielectric with dielectric constant 2 . 9 is inserted into the 59 . 3 F capacitor (lower- centered capacitor) while the battery is con- nected. What is the charge on the 84 F lower-right capacitor? Correct answer: 8299 . 2 C. Explanation: Since the battery is still connected, the volt- age will remain the same. Thus the charge is simply Q 4 = V ab C 4 = (98 . 8 V) (84 F) = 8299 . 2 C . 005 (part 4 of 4) 10.0 points If the battery is removed before the dielectric in the above question is inserted, what will be the charge on the 84 F lower-right capacitor?...
View Full Document

This note was uploaded on 11/03/2009 for the course PHY 303L taught by Professor Turner during the Spring '08 term at University of Texas at Austin.

Page1 / 10

Practice Midterm 02-solutions - sanne (as42476) Practice...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online