Exam 31: Electromagnetic Oscillations and Alternating Current

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 potential difference across the capacitor?

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 energy stored in the electric field of the capacitor is a maximum 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:

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:

The reactance in ohms of a 35- $\mu$ F capacitor connected to a 400-Hz generator 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 voltage (in volts) across the inductor is:

In a purely resistive circuit the 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:

An ac generator produces 10 V (rms) at 400 rad/s. It is connected to a series RL circuit (R = 17.3 $\Omega$ L = 0.025 H). The rms current is:

In an RLC series circuit, the source voltage is leading the current at a given frequency f. If f is lowered slightly, then the circuit impedance will:

The primary of a 3:1 step-up transformer is connected to a source and the secondary is connected to a resistor R. The power dissipated by R in this situation is P. If R is connected directly to the source it will dissipate a power of:

An RLC circuit has a sinusoidal source of emf. The average rate at which the source supplies energy is 5 nW. This must also be:

A coil has a resistance of 60 $\Omega$ and an impedance of 100 $\Omega$ . Its reactance, in ohms, is:

An RLC series circuit has R = 4 $\Omega$ , X_C = 3 $\Omega$ , and X_L = 6 $\Omega$ . The impedance of this circuit is:

The angular frequency of a certain RLC series circuit is $\omega$ ₀. A source of sinusoidal emf, with angular frequency $\omega$ , is inserted into the circuit and $\omega$ is varied while the amplitude of the source is held constant. For which of the following values of $\omega$ is the amplitude of the current oscillations the greatest?

In a purely capacitive circuit the current:

The rms value of an ac current is:

When the amplitude of the oscillator in a series RLC circuit is doubled:

A 35- $\mu$ F capacitor is connected to an ac source of emf with a frequency of 400 Hz and a maximum emf of 20 V. The maximum current is:

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