Exam 31: Electromagnetic Oscillations and Alternating Current

A charged capacitor and an inductor are connected in series. At time t = 0 the current is zero, but the capacitor is charged. If T is the period of the resulting oscillations, the next time, after t = 0 that the voltage across the inductor is a maximum is:

The total energy in an LC circuit is 5.0 *10^-6 J. If C = 15 $\mu$ F the charge on the capacitor is:

An ac generator producing 10 V (rms) at 200 rad/s is connected in series with a 50- $\Omega$ resistor, a 400-mH inductor, and a 200- $\mu$ F capacitor. The rms current in amperes is:

In a sinusoidally driven series RLC circuit, the inductive resistance is X_L = 200 $\Omega$ , the capacitive reactance is X_C = 100 $\Omega$ , and the resistance is R = 50 $\Omega$ . The current and applied emf would be in phase if:

An RLC series circuit has L = 100 mH and C = 1 $\mu$ F. It is connected to a 1000-Hz source emf is foundto lead the current by 75 $\degree$ . The value of R is:

A step-down transformer is used to:

An LC circuit has an inductance of 15 mH and a capacitance of 10 $\mu$ F. At one instant the charge on the capacitor is 25 $\mu$ C. At that instant the current is changing at the rate:

In an RLC series circuit, which is connected to a source of emf $\varepsilon$ _mcos( $\omega$ t), the current lags the voltage by 45 $\degree$ if:

An electric motor, under load, has an effective resistance of 30 $\Omega$ and an inductive reactance of 40 $\Omega$ . When powered by a source with a maximum voltage of 420 V, the maximum current is:

The average power supplied to the circuit shown passes through a maximum when which one of the following is increased continuously from a very low to a very high value?

In a series RLC circuit the rms value of the generator emf is E and the rms value of the current is i. The current lags the emf by $\phi$ . The average power supplied by the generator is given by:

An RLC circuit has a resistance of 200 $\Omega$ and an inductance of 15 mH. Its oscillation frequency is 7000 Hz. At time t = 0 the current is 25 mA and there is no charge on the capacitor. After five complete cycles ther current is:

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:

The graphs show the total electromagnetic energy in two RLC circuits as functions of time. Which of the following statements might be true?

A capacitor in an LC oscillator has a maximum potential difference of 15 V and a maximum energy of 360 $\mu$ J. At a certain instant the energy in the capacitor is 40 $\mu$ J. At that instant what is the emf induced in the inductor?

Which of the following has the greatest effect in decreasing the oscillation frequency of an LC circuit? Using instead:

An ac generator producing 10 V (rms) at 200 rad/s is connected in series with a 50- $\Omega$ resistor, a 400-mH inductor, and a 200- $\mu$ F capacitor. The rms voltage (in volts) across the resistor is:

In the circuit shown, switch S is first pushed up to charge the capacitor. When S is then pushed down, the current in the circuit will oscillate at a frequency of:

The reactance in ohms of a 35- $\mu$ F capacitor connected to a 400-Hz generator is:

The electrical analog of a spring constant k is: