# q5_sol - V A-V B =-R A B E · d r =-E R z A z B dz =-E ( z...

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Quiz 5 Phys. 2306 F09 Crn94823 You may use your text book, notes, and a calculator. Two very large area parallel, conducting plates A,B are kept at a potential diﬀerence Δ V by a battery. The plates are separated by a distance d. Small holes are drilled in the plates so that particles traveling perpendicular to the plates can pass through the holes. Electron 1 traveling from A to B is accelerated from 3.00 × 10 6 m/s to 8.00 × 10 6 m/s. Electron 2 traveling from B to A is slowed from speed v to zero. You may use q e = - 1 . 60 × 10 - 19 C and m e = 9 . 11 × 10 - 31 kg. 1) The electric ﬁeld between the plates points from? a) A to B b) B to A The speed of electron 1 increases as it travels from A to B. Since electrons have nega- tive charge, the electric ﬁeld points from B to A, b. 2) Which plate is at the higher potential? a) A b) B Pick E = E 0 k so that E 0 is a positive constant and going from B to A means you are going in the direction of increasing z. Then,

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Unformatted text preview: V A-V B =-R A B E · d r =-E R z A z B dz =-E ( z A-z B ) < 0, b. 3) What is Δ V in volts? a) 7.42 b) 15.7 c) 157. d) 314. e) none of these Note q e =-e . Use conservation of energy on electron 1, so, 0 . 5 m ( v 2 B-v 2 A )+-e ( V B-V A ) = 0. Thus, Δ V = (0 . 5 m/e )( v 2 B-v 2 A ) = 157 V, c. 1 4) What is the speed v in 10 6 m/s? a) 7.42 b) 5.26 c) 3.71 d) 2.14 e) none of these From conservation of energy and the fact that the ﬁnal KE= 0, one gets 0 . 5 mv 2 = e Δ V . So v = q (2 e/m )Δ V = 7 . 42 × 10 6 m/s, a. 5) What is the surface charge density on the surface of the positive plate closest to the negative plate in terms of d, ± , Δ V ? a) ± Δ V d b) 2 ± Δ V d c) ± Δ V 2 d d) Δ V d± d) none of these E = σ/± = Δ V/d , so σ = ± Δ V/d , a. 2...
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## This note was uploaded on 12/24/2011 for the course PHYS 2306 taught by Professor Ykim during the Fall '06 term at Virginia Tech.

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q5_sol - V A-V B =-R A B E · d r =-E R z A z B dz =-E ( z...

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