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Common02_solution

# Common02_solution - Physics 121 Honors Name Common Exam 2...

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Physics 121 Honors Common Exam 2 Spring 2003 Name: Section: Closed book exam. Only one 8 . 5 00 × 11 00 formula sheet (front and back side) can be used. Calculators are allowed. Use the scantron forms (pencil only!) for the multiple choice problems. Circle the answers on the examination sheet as well, and return it together with the scantron form. Use the back of these pages, or attach your own pages with solutions for problems that require calculations. The eight multiple-choice problems are 6 points each. Partial credit (up to 4 points) will be given for multiple-choice problems, if you provide a detailed solution on the examination sheets. The four work-out problems are 13 points each. The nominal number of points is 100. Clearly print your ﬁrst and last name and indicate your section number on both the scantron form and the examination sheet. Good luck! Multiple-Choice Problems Problem 1: What is the electric potential at point P , located at the center of the square of point charges? The distance is d = 15 cm, and the charges are q 1 = + 21 μ C, q 2 = - 56 C, q 3 = + 47 C, and q 4 = + 21 C. A) - 7 . 6 × 10 5 V B) - 5 . 4 × 10 5 V C) + 2 . 0 × 10 6 V D) + 2 . 8 × 10 6 V E) + 1 . 9 × 10 7 V r = d 2 V = 1 4 πε 0 r ( q 1 + q 2 + q 3 + q 4 ) = 2 4 0 d ( q 1 + q 2 + q 3 + q 4 ) = 2 . 80 × 10 6 V Problem 2: The Bohr model of the Hydrogen atom states that the single electron can exist only in certain allowed orbits around the proton. The radius of each Bohr orbit is r = r 0 n 2 , where r 0 = 0 . 0529 nm and n = 1 , 2 , 3 ,... . Calculate the electric potential energy of a hydrogen atom when the electron is in the third ( n = 3) allowed orbit! A) 3.0 eV B) 6.8 eV C) 9.1 eV D) 27 eV E) 6.3 GeV U = eV = e ± e 4 0 r 0 n 2 = 3 eV

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Problem 3: A capacitor consists of two concentric shells of inner radius a = 2 . 0 cm and outer radius b = 5 . 0 cm. The capacitor has a charge of q = 24 . 6 nC. How much energy is stored in the electric ﬁeld of this charged conductor?
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Common02_solution - Physics 121 Honors Name Common Exam 2...

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