su10FinalS

# su10FinalS - Final Exam Solutions Part A Multiple choice...

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Unformatted text preview: Final Exam Solutions Part A. Multiple choice questions. Check the best answer. Each question carries a value of 4 points. The Frst four questions concern the fundamental equations of electromagnetism, numbered 1-5 here: 1. E ⋅ d A ∫ = 4 π kQ enc 2. E ⋅ d r ∫ = − ( ∂ B / ∂ t ) ⋅ d A ∫ 3. B ⋅ d A ∫ = 4. B ⋅ d r ∫ = μ I linked + ε ( ∂ E / ∂ t ) ⋅ d A ∫ ⎡ ⎣ ⎤ ⎦ 5. F = q ( E + v × B ) 1. If none of the quantities in the equations depend on time, which equation forbids lines of the E-Feld to form closed curves? 1 only. √ 2 only. 4 only. 5 only. 2. Which equation requires lines of the B-Feld to form closed curves? 2 only. 2 and 4. √ 3 only. 5 only. Physics 54 Summer 2010 1 3. Which equations do we use to show the existence of electromagnetic waves? 2 and 4 only. 2, 4 and 5. √ All of 1-4. All Fve. 4. Which equations describe phenomena that make possible an industrial society using electric generators and motors? 1 and 3. 4 and 5. 2 and 4. √ 2 and 5. [2 for generators, 5 for motors.] 5. Shown are two circuits to control the brightness of a light bulb. In the top circuit the resistance R can be varied. In the bottom circuit, the inductance L can be varied. When the bulb is at the same brightness in both cases: Physics 54 Summer 2010 2 The generator supplies less power in the top circuit. √ The generator supplies less power in the bottom circuit. [It supplies no power to the inductor.] The generator supplies the same power in both circuits. In which case the generator supplies more power depends on its frequency. E L E R 6. Which is NOT a property of an e-m wave emitted by a small distant source? √ The magnitude of each of the Felds in the wave falls of as the inverse square of the distance. [Inverse Frst power.] The magnitudes obey E = cB . If the wave moves in the + x-direction, and E is in the z-direction, then B is in the – y-direction. The energy density in the E-Feld is equal to that in the B-Feld. 7. Sodium lamps shine with light from two spectral lines at about 600 nm, differing in wavelength by 0.6 nm. Consider a grating with rulings 1500 nm apart. The two lines cannot be seen in 2nd order. [They can.] To resolve these lines in 1st order, the grating must have at least 2000 rulings. [1000 is enough.] The angle at which these lines will be seen in 1st order is given by sin θ ≈ 0.6 . [0.4.] √ None of the above is true. 8. Which of the following is NOT a consequence of the uncertainty principle? The state of an atomic electron cannot be speciFed in terms of its position and velocity. √ No state of an atomic electron can have a deFnite energy. [The ground state has deFnite energy.] The program of Newtonian mechanics can only be carried out as an approximation for large systems....
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su10FinalS - Final Exam Solutions Part A Multiple choice...

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