Homework 7-solutions

Homework 7-solutions - gonzales(pag757 – Homework 7 –...

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

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.

Unformatted text preview: gonzales (pag757) – Homework 7 – Hoffmann – (56745) 1 This print-out should have 12 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points The emf of a battery is E = 19 V . When the battery delivers a current of 0 . 7 A to a load, the potential difference between the terminals of the battery is 17 V volts. Find the internal resistance of the battery. Correct answer: 2 . 85714 Ω. Explanation: Given : E = 19 V , V load = 17 V , and I = 0 . 7 A . The potential difference across the internal resistance is E - V load , so the internal resis- tance is given by r = E - V load I = 19 V- 17 V . 7 A = 2 . 85714 Ω . 002 10.0 points Four copper wires of equal length are con- nected in series. Their cross-sectional areas are 0 . 8 cm 2 , 2 . 5 cm 2 , 1 . 3 cm 2 , and 7 cm 2 . If a voltage of 142 V is applied to the ar- rangement, determine the voltage across the 2 . 5 cm 2 wire. Correct answer: 22 . 1694 V. Explanation: Let : A 1 = 0 . 8 cm 2 , A 2 = 2 . 5 cm 2 , A 3 = 1 . 3 cm 2 , A 4 = 7 cm 2 , and V tot = 142 V . The resistance of the copper wire is propor- tional to the length of the wire and inversely proportional to the cross sectional area of the wire. Since the lengths are the same, and the current i is the same for all resistors connected in series, taking r ∝ 1 A , etc, we have i = V tot r 1 + r 2 + r 3 + r 4 = V 2 r 2 , where V tot is the difference in voltage across all for wires and V 2 is the difference in voltage across the second wire only. Solving for V 2 , we have V 2 = r 2 r 1 + r 2 + r 3 + r 4 V tot = 1 A 2 1 A 1 + 1 A 2 + 1 A 3 + 1 A 4 V tot = 1 2 . 5 cm 2 1 . 8 cm 2 + 1 2 . 5 cm 2 + 1 1 . 3 cm 2 + 1 7 cm 2 × (142 V) = 22 . 1694 V . 003 10.0 points Four resistors are connected as shown in the figure. 2 1 Ω 5 2 Ω 8 8 Ω 94 V 37Ω S 1 a b c d Find the resistance between points a and b . Correct answer: 37 . 5165 Ω. Explanation: gonzales (pag757) – Homework 7 – Hoffmann – (56745) 2 R 1 R 3 R 4 E B R 2 S 1 a b c d Let : R 1 = 21 Ω , R 2 = 37 Ω , R 3 = 52 Ω , R 4 = 88 Ω , and E B = 94 V . Ohm’s law is V = I R . A good rule of thumb is to eliminate junc- tions connected by zero resistance....
View Full Document

{[ snackBarMessage ]}

Page1 / 8

Homework 7-solutions - gonzales(pag757 – Homework 7 –...

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

View Full Document
Ask a homework question - tutors are online