UnitExam4Csolutions

# UnitExam4Csolutions - ID C UCSD Physics 2B Answer Section...

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ID: C 1 UCSD Physics 2B Unit Exam 4C Magnetism & Induction Answer Section MULTIPLE CHOICE 1. ANS: C B = μ 0 In = 0 IN / L L = 0 IN B = 1.26 × 10 6 H / m Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ 3.5 A () 69 3.5 × 3 T = 8.7 × 2 m TOP: SOLENOID 2. ANS: A The magnetic flux is the product of the coil area A , the number of turns N , the magnetic field strength B and the cosine of the angle at which the field lines penetrate the coil: Φ= N B A = NBA cos θ N = Φ BA cos = 0.75 Wb 0.5 T × 2 Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ 2 cos60 = 300 TOP: FLUX 3. ANS: C Lenz's Law says that the induced current flows in such a way as to oppose the change in magnetic field. As the magnet falls through the copper tube, current begins to swirl beneath it making its own magnetic field which points in the opposite direction, slowing the magnet's fall. TOP: LENZ DEMO 4. ANS: B The magnetic moment of the coil = NIA = NI π R 2 Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ The torque on the coil τ = × B = Bsin ϑ = NI R 2 Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ = 200 7.5 A 3.14 25 × 2 m Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ 2 0.35 T sin53 = 82 N m TOP: DIPOLE TORQUE 5. ANS: C = = R 2 Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ = 2 2.5 A × 2 m Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ 2 = 0.157 A m 2 TOP: DIPOLE MOMENT

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ID: C 2 6. ANS: C Force between two parallel wires of length L separated by distance r carrying different currents : F = μ 0 I 1 I 2 L 2 π r . So force per unit length for two wires carrying the same current: F L = 0 I 2 2 r = 1.26 × 10 6 H / m Ê Ë Á Á Á ˆ ¯ ˜ ˜ ˜ A () 2 23 .14 0.01 m = 2.01 × 3 N m TOP: PARALLEL WIRES 7. ANS: A F = q v × B whose magnitude F = qvB sin ϑ .
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UnitExam4Csolutions - ID C UCSD Physics 2B Answer Section...

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