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Unformatted text preview: Version 079 – Final – shih – (56310) 1 This printout should have 35 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A rod starts from rest at the top of an inclined plane at t = 0. The rails have negligi ble resistance. There is a constant, vertically directed magnetic field of magnitude 1 T. The acceleration due to gravitation is 9 . 81 m / s 2 . 3 Ω v . 8 kg 1 T sliding rod 24 m Viewed from above v 30 ◦ 1 T Viewed from the side What will be the terminal speed of the rod? 1. 1.02986 2. 4.84444 3. 3.29554 4. 2.725 5. 1.26157 6. 2.90667 7. 4.63435 8. 0.68125 9. 0.823885 10. 4.74558 Correct answer: 2 . 725 cm / s. Explanation: R v m B sliding rod ℓ Viewed from above Let : B = 1 T , R = 3 Ω , g = 9 . 81 m / s 2 , ℓ = 24 m , and θ = 30 ◦ . v θ B Viewed from the side The induced emf is E = B ℓ v cos θ . Using Ohm’s law, the current in the circuit due to the induced emf is I = E R = B ℓ v cos θ R . Then the force due to the current is F m = I ℓ B = B 2 ℓ 2 v cos θ R . Applying Newton’s 2 nd law to the rod, mg sin θ F m cos θ = m dv dt g sin θ F m m cos θ = dv dt . Version 079 – Final – shih – (56310) 2 As the rod reaches the terminal speed, dv dt = 0, and g sin θ = F m m cos θ g sin θ = B 2 ℓ 2 v cos θ mR cos θ . Thus v = mg R sin θ B 2 ℓ 2 cos 2 θ = (0 . 8 kg) (9 . 81 m / s 2 ) (3 Ω) sin 30 ◦ (1 T) 2 (24 m) 2 cos 2 30 ◦ × 100 cm 1 m = 2 . 725 cm / s . keywords: 002 (part 1 of 3) 10.0 points ONLY DO PART 1 OF THIS 3 PART QUESTION!!!!! Consider just four of the energy levels in a certain atom, as shown in the diagram below. n = 1 n = 2 n = 3 n = 4 How many spectral lines will result from all possible transitions among these levels? Which transition corresponds to the highest frequency light emitted? Which transition corresponds to the lowestfrequency? 1. three; level 2 to level 1 transition; level 4 to level 3 transition. 2. six; level 4 to level 1 transition; level 4 to level 3 transition. correct 3. three; level 4 to level 1 transition; level 4 to level 3 transition. 4. three; level 4 to level 3 transition; level 2 to level 1 transition. Explanation: Six transitions are possible, as shown. n = 1 n = 2 n = 3 n = 4 The highestfrequency transition is from quantum level 4 to level 1. The lowest frequency transition is from quantum level 4 to level 3. 003 (part 2 of 3) 0.0 points An electron deexcites from the fourth quan tum level to the third and then directly to the ground state. Two photons are emitted. How does the sum of their frequencies com pare to the frequency of the single photon that would be emitted by deexcitation from the fourth level directly to the ground state?...
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 Spring '10
 TSOI
 Physics, Electric charge, Final – shih

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