31 - EM Oscillations & AC

# 31 - EM Oscillations & AC - Q1 A charged capacitor and...

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Q1) A charged capacitor and an inductor are connected in series. At time t = 0 s, the current is zero and the capacitor is fully charged. If T is the period of the resulting oscillations, the first time after t = 0 that (a) the charge on the capacitor is a maximum and (b) the energy stored in the magnetic field of the inductor is a maximum is 1) (a) T (b) T/4 2) (a) T (b) T/2 3) (a) T/2 (b) T/4 4) (a) T/2 (b) T/2 5) (a) T/4 (b) T Q2) A charged capacitor and an inductor are connected in series. At time t = 0 s, the current is zero and the capacitor is fully charged. If T is the period of the resulting oscillations, the first time after t = 0 that (a) the voltage across the capacitor is a maximum (with its initial polarity) and (b) the current is a maximum is 1) (a) T (b) T/4 2) (a) T (b) T/2 3) (a) T/2 (b) T/4 4) (a) T/2 (b) T/2 5) (a) T/4 (b) T Q3) The figure below shows three oscillating LC circuits with identical inductors and capacitors. Rank the circuits according to the time taken to fully discharge the capacitors during the oscillations, greatest first. 1) a, b, c 2) a, c, b 3) b, c, a 4) b, a, c 5) c, a, b

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Q4) For each of the curves of q(t) in the figure below for an LC circuit, determine the least positive phase constant in the equation cos( ) q Q t   required to produce the curve. 1) (a) 3  (b)  (c)  2) (a) 3  (b)  (c)  3) (a)  (b)  (c) 3  4) (a)  (b) 3  (c)  5) (a)  (b)  (c) 3  Q5) Which of the following has the greatest effect in decreasing the oscillation frequency of an LC circuit? Using instead: 1) L/2 and C/2 2) L/2 and 2C 3) 2L and C/2 4) 2L and 2C 5) none of these Q6) In an oscillating LC circuit, the total stored energy is U and the maximum charge on the capacitor is Q. When the charge on the capacitor is Q/2, the energy stored in the inductor is: 1) U/2 2) U/4 3) (4/3)U 4) 3U/2 5) 3U/4
Q7) The figure below shows graphs of the capacitor voltage v C for LC circuits 1 and 2, which contain identical capacitances and have the same maximum charge Q. Are (a) the inductance and (b) the maximum current I in circuit 1 greater than, less than, or the same as those in circuit 2? 1) (a) greater than (b) greater than 2) (a) greater than (b) less than 3) (a) less than (b) greater than 4) (a) less than (b) less than

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Q8) Which one of the following graphs illustrates how capacitive reactance varies with frequency? Q9) Which one of the following graphs shows how the inductive reactance varies with frequency?
Q10) For a capacitor in an ac circuit, ho w much energy is stored in the capacitor at the instant when current is zero? 1) zero 2) maximum 3) half of the maximum amount 4) impossible to tell without the phase angle Q11) An alternating emf source is connected, in turn, to a resistor, a capacitor, and then an inductor. Once connected to these devices, the driving frequency f d is varied and the amplitude I of the resulting current through the device is measured and plotted. Which of the three plots in the

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