HW #3-solutions - zapata(jz883 – HW#3 – Antoniewicz...

Info iconThis preview shows pages 1–2. 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: zapata (jz883) – HW #3 – Antoniewicz – (56495) 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 The total charge that an automobile battery can supply without being recharged is given in terms of Ampere-hours. A typical 12-V battery has a rating of 72 A · h . Suppose you forget to turn off the headlights in your parked automobile. If each of the two headlights draws 1 . 7 A , find out the time before your battery is “dead”. Correct answer: 21 . 1765 h. Explanation: Let : rating = 72 A · h and I = 1 . 7 A . If only one of the two headlights is left on, the time before the battery dies is given by T 1 = rating I = 72 A · h 1 . 7 A = 42 . 3529 h . Thus the required time is 21 . 1765 h . 002 10.0 points A commercial capacitor is constructed as in the figure. This particular capacitor is made from two stripes of aluminum separated by a strip of paraffin-coated paper. Each strip of foil and paper is 5 . 88 cm wide. The foil is . 0049 mm thick, and the paper is 0 . 0258 mm thick and has a dielectric constant of 3 . 8. Metal Foil Paper What length should the strips be if a capac- itance of 6 . 24 × 10 − 8 F is desired before the capacitor is rolled up? (Use the parallel-plate formula. Adding a second strip of paper and rolling up the capacitor doubles its capaci- tance by allowing both surfaces of each strip of foil to store charge.) Correct answer: 0 . 814142 m. Explanation: Let : k = 3 . 8 , w = 5 . 88 cm = 0 . 0588 m , ǫ = 8 . 85 × 10 − 12 C 2 / N · m 2 , d 1 = 0 . 0049 mm = 4 . 9 × 10 − 6 m , d 2 = 0 . 0258 mm = 2 . 58 × 10 − 5 m , and C = 6 . 24 × 10 − 8 F . Before the capacitor is rolled, the capacitor of this parallel plate capacitor is C = k ǫ A d = k ǫ w L d , where A is the surface area of one side of a foil strip. Thus the required length is L = C × d k ǫ w = (6 . 24 × 10 − 8 F) × (2 . 58 × 10 − 5 m) (3 . 8) (8 . 85 × 10 − 12 C 2 / N · m 2 ) (0 . 0588 m) = . 814142 m . 003 10.0 points An incandescent bulb has a resistance of 22 Ω when it is at room temperature (25 ◦ C) and 478 Ω when it is hot and delivering light to the room. The temperature coefficient of re- sistivity of the filament is 0 . 005 ( ◦ C) − 1 , where the base resistance R is determined at 0 ◦ C....
View Full Document

This note was uploaded on 10/01/2010 for the course PHYSICS PHY 303 L taught by Professor Antoniewicz during the Spring '10 term at Texas Pan American.

Page1 / 6

HW #3-solutions - zapata(jz883 – HW#3 – Antoniewicz...

This preview shows document pages 1 - 2. Sign up to view the full document.

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