UnitExam1Asolutions

# UnitExam1Asolutions - ID A UCSD Physics 2B Answer Section...

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ID: A 4 UCSD Physics 2B Unit Exam 1A Charges, Force & Fields Answer Section MULTIPLE CHOICE 1. ANS: D The charge for each species is the number of particles times the charge per particle. The total net charge is the sum of these: Q net = n p q p + n e q e = n p e + Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ + n e e Ê Ë Á Á ˆ ¯ ˜ ˜ = n p n e Ê Ë Á Á ˆ ¯ ˜ ˜ e + = 6.02 × 10 23 1.99 × 24 Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ + 1.60 × 19 C Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ =− 1.388 × Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ + × C Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ 2.22 × 5 C TOP: ELEMENTARY CHARGE 2. ANS: B By definition, E = F q = 11.9 N 25.0 × 6 C = 4.76 × 5 N C TOP: ELECTRIC FIELD 3. ANS: D Very basic stuff - like charges repel, unlike charges attract. TOP: CHARGE CONCEPT 4. ANS: B This formula is worked out in the text. All you have to do is find total ring charge Q : E = kxQ x 2 + a 2 Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ 3/2 = kx 2 π a λ () x 2 + a 2 Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ = 1 4 πε 0 x 2 a x 2 + a 2 Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ = xa 2 ε 0 x 2 + a 2 Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ = 36.0 × 2 m Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ 27.0 × 2 m Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ 1.32 × 4 C / m Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ 28 .8 5 × 12 C 2 / Nm 2 Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ 36.0 × 2 m Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ 2 + 27.0 × 2 m Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ 2 Ê Ë Á Á Á Á Á Á ˆ ¯ ˜ ˜ ˜ ˜ ˜ ˜ = 7.96 × 6 N / C TOP: ELECTRIC FIELD RING 5. ANS: E Fundamental properties of conductors : Electric field is zero inside Electric field is perpendicular at surface Excess charge must reside at surface only TOP: CONDUCTOR FIELD CONCEPT

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ID: A 2 6. ANS: B For a single
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UnitExam1Asolutions - ID A UCSD Physics 2B Answer Section...

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