PHY 2049 Physics II n n n Tutoring

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

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

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

Alternating Currents n A resistance The current and voltage are in phase

Capacitor: AC response The current leads the voltage

Inductor: AC response n The current lags the voltage

HITT n n A capacitor in an LC oscillator has a maximum potential difference of 15 V 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 E. 20 V B. 5 V C. 10 V D. 15 V

A different problem n n n An LC circuit has a capacitance of 30 μF and an inductance of 15 m. H. At time t = 0 the charge on the capacitor is 10 μC and the current is 20 m. A. The maximum charge on the capacitor is: A. 8. 9 μC B. 10 μC C. 12 μC D. 17 μC E. 24 μC

Yet different n n n n A 45 -m. H inductor is connected to a source of sinusoidal emf with a frequency of 400 Hz and a maximum emf of 20 V. The maximum current is: A. 0 B. 0. 18 A C. 1. 1 A D. 360 A E. 2300 A ans: B

RLC circuit

RLC circuit Inductive Capacitive In resonance

e = E sin ωt i = io sin (ωt –φ) Capacitor current leads Power = I 2 R = ermsirmscosφ (cos φ =R/Z)

Resonance

Transformers