homework 1

# homework 1 - montes(dam2772 Homework1 shih(56310...

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

montes (dam2772) – Homework1 – shih – (56310) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points The diagram above shows an isolated, pos- itive charge Q. Point B is twice as far away from Q as point A. + Q A B What is the ratio of the electric field strength at point A to the electric field strength at point B? 1. 2 to 1 2. 4 to 1 correct 3. 1 to 2 4. 8 to 1 5. 1 to 1 Explanation: The electric field drops as 1 r 2 from a point charge. The electric field at point A would be Q d 2 where d is the distance between the charge and point A. The electric field at point B would be Q (2 d ) 2 . The ratio of E A to E B is then 1 1 / 4 or 4 to 1. 002 10.0points When combing your hair, you scuff electrons from your hair onto the comb. Is your hair then positively or negatively charged? What about the comb? 1. Neither is charged. 2. Both are negatively charged. 3. Both are positively charged. 4. positively charged; negatively charged correct 5. negatively charged; positively charged Explanation: Excess electrons rubbed from your hair leave it positively charged. Excess electrons on the comb give it a negative charge. 003 10.0points A particle with charge 5 μ C is located on the x -axis at the point 4 cm , and a second particle with charge 6 μ C is placed on the x -axis at 8 cm . 2 4 6 8 10 2 4 6 8 10 5 μ C 6 μ C 2 μ C x (cm) What is the magnitude of the total elec- trostatic force on a third particle with charge 2 μ C placed on the x -axis at 2 cm ? The Coulomb constant is 8 . 9875 × 10 9 N · m 2 / C 2 . Correct answer: 235 . 473 N. Explanation: Let : q 1 = 5 μ C = 5 × 10 6 C , q 2 = 6 μ C = 6 × 10 6 C , q 3 = 2 μ C = 2 × 10 6 C , x 1 = 4 cm = 0 . 04 m , x 2 = 8 cm = 0 . 08 m , and x 3 = 2 cm = 0 . 02 m . Coulomb’s law (in vector form) for the elec- tric force exerted by a charge q 1 on a second charge q 3 , written vector F 13 is vector F 13 = k e q 1 q 3 r 2 ˆ r 13 , where ˆ r 13 is a unit vector directed from q 1 to q 3 ; i.e. , vectorr 13 = vectorr 3 vectorr 1 . x 13 = x 3 x 1 = ( 2 cm) ( 4 cm) = 0 . 02 m x 23 = x 3 x 2

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

View Full Document
montes (dam2772) – Homework1 – shih – (56310) 2 = ( 2 cm) (8 cm) = 0 . 1 m ˆ x 13 = x 3 x 1 radicalbig ( x 3 x 1 ) 2 = +ˆ ı ˆ x 23 = x 3 x 2 radicalbig ( x 3 x 2 ) 2 = ˆ ı Since the forces are collinear, the force on the third particle is the algebraic sum of the forces between the first and third and the second and third particles. vector F = vector F 13 + vector F 23 = k e bracketleftbigg q 1 r 2 13 ˆ r 13 + q 2 r 2 23 ˆ r 23 bracketrightbigg q 3 = 8 . 9875 × 10 9 N · m 2 / C 2 × bracketleftbigg (5 × 10 6 C) (0 . 02 m) 2 (+ˆ ı ) + ( 6 × 10 6 C) ( 0 . 1 m) 2 ( ˆ ı ) bracketrightbigg × (2 × 10 6 C) = 224 . 688 N + (10 . 785 N) = 235 . 473 N , with a magnitude of 235 . 473 N .
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern