PHY 2049: Physics II

1. PHY 2049: Physics II • Tutoring Center is open in room NPB 1215, M-F 12:00AM -4:00PM. It is free. • The following hitt numbers need to register. Please do so ASAP. • 402407 405767 416479 • 402614 406876 417029 • 432808 411209 420713 • 432798

2. Ch. 31 Electromagnetic Oscillations • RC, RL, LC circuits • Driven damped Oscillations • Resonance • Series RLC circuits • Power • Transformer

3. Last time • LC circuit • Analogous to a pendulum • L m • q x • C 1/k • Be careful with ωt in radians (not degrees)

4. Alternating Currents • A resistance The current and voltage are in phase

5. Capacitor: AC response The current leads the voltage

6. Inductor: AC response • The current lags the voltage

7. HITT • A capacitor in an LC oscillator has a maximum potential difference of 15V and a maximum energy of 360 μJ. At a certain instant the energy in the capacitor is 40 μJ. At that instant what is the potential difference across the capacitor? • A. zero B. 5V C. 10V D. 15V E. 20V

8. A different problem • An LC circuit has a capacitance of 30 μF and an inductance of 15mH. At time t = 0 the charge on the capacitor is 10 μC and the current is 20mA. The maximum charge on the capacitor is: • A. 8.9 μC • B. 10 μC • C. 12 μC • D. 17 μC • E. 24 μC

9. Yet different • A 45-mH inductor is connected to a source of sinusoidal emf with a frequency of 400 Hz and a maximum emf of 20V. The maximum current is: • A. 0 • B. 0.18A • C. 1.1A • D. 360A • E. 2300A • ans: B

10. RLC circuit

11. RLC circuit Inductive Capacitive In resonance

12. e = E sin ωt i = io sin (ωt –φ) Capacitor current leads Power = I2R = ermsirmscosφ (cos φ =R/Z)

14. Resonance

15. Transformers