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Unformatted text preview: 1 Physics 4B FINAL EXAM Chapters 22 - 34 Spring 1997 Name:_________________________________________ Posting Code _____ _____ _____ Solve the following problems in the space provided. Use the back of the page if needed. Each problem is worth 10 points. You must show your work in a logical fashion starting with the correctly applied physical principles which are on the last page. Your score will be maximized if your work is easy to follow because partial credit will be awarded. 1. At some instant the nucleus of a helium atom and its orbiting electrons are oriented as shown. Find the electric force (magnitude and direction) felt by the electron at the bottom right. The electric forces due to the point charges are given by Coulomb’s Rule: F 1 = k (e)(e) r 1 2 = (9x10 9 ) (1.6x10- 19 ) 2 (0.193x10- 9 ) 2 = 6.19x10- 9 N F 2 = k (2e)(e) r 2 2 = (9x10 9 ) 2(1.6x10- 19 ) 2 (0.141x10- 9 ) 2 = 2.32x10- 8 N Adding the vector components: F x = F 1- F 2 cos30˚ = - 1.39x10- 8 N and F y = F 2 sin30˚ = 1.16x10- 8 N The magnitude and direction are: F = F x 2 + F y 2 = 1.81x10- 8 N and θ = arctan F y F x = 40˚ above the -x axis. 2. A 5.00μC charge is located 3.00cm upward from the center of the base of a cone of radius 2.00cm and height 5.00cm. Find the total electric flux leaving the cone. Applying Gauss's Law to the entire cone, r E • d r A ∫ = q enclosed ε o ⇒ Φ total = q enclosed ε o ⇒ Φ total = 5.00x10- 6 8.85x10- 12 = 5.65x10 5 V ⋅ m . 0.100nm 30˚ +2 e- e- e 45˚ 0.141nm 0.193nm x y 1 F 2 F F θ 5μC 5cm 3cm 2cm 2 3. Find the potential due to a 20.0cm long rod that has a linear charge density of 2.00μC/m at a pointhas a linear charge density of 2....
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- Fall '09
- Work, Magnetic Field