Capacitor Charging Phase Quiz

R-C Filters

• At low frequencies, input voltage is equal to output voltage in an R-C low pass filter.
• At high frequencies, output voltage is equal to zero in an R-C low pass filter.
• A high-pass R-C filter can be constructed by reversing the positions of the capacitor and resistor.
• At very high frequencies, the reactance of the capacitor is very small, and the short-circuit equivalent can be substituted, resulting in Vo = Vi.
• At f = 0 Hz, the reactance of the capacitor is quite high, and the open-circuit equivalent can be substituted, resulting in Vo = 0V.

Tuning and Resonance

• The tuning process is the reason for the terminology "tuned circuit".
• When the response is at or near the maximum, the circuit is said to be in a state of resonance.
• A resonant electrical circuit must have both inductance and capacitance.
• Resistance will always be present due to the lack of ideal elements or to control the shape of the resonance curve.
• Mechanical impulses applied to a mechanical system at the proper frequency will cause the system to enter a state of resonance.

Capacitors

• The voltage across a capacitor in a dc network is essentially equal to the applied voltage after five time constants of the charging phase.
• The transient or charging phase of a capacitor has essentially ended after five-time constants.
• The current of a capacitive dc network is essentially zero amperes after five time constants of the charging phase.
• During the charging phase, the major change in voltage and current occurs during the first time constant.
• A capacitor can be replaced by an open-circuit equivalent once the charging phase in a dc network has passed.
• An ideal capacitor does not dissipate any of the energy supplied to it, storing it in the form of an electric field between the conducting surfaces.

Inductors

• The inductor takes on the characteristics of an open circuit at the instant the switch is closed.
• The current cannot change instantaneously in an inductive network.

Superposition Theorem

• The superposition theorem is one of the most powerful in this field.

Decibel (dB)

• The unit decibel (dB) is used to define levels of audio, voltage gain, energy, field strength, and so on.
• The decibel is defined by a logarithmic expression.
• Normal conversation occurs at about 60 dB, while damage to the eardrum can begin at 100 dB and higher.
• The use of bel (B) and decibel (dB) is in recognition of Alexander Graham Bell's research and development of electronic devices.

Logarithmic Function Applications

• The response of a system can be plotted for a range of values that may otherwise be impossible or unwieldy with a linear scale.
• Levels of power, voltage, and the like can be compared without dealing with very large or very small numbers.
• A number of systems respond to outside stimuli in a nonlinear logarithmic manner.
• The response of a cascaded or compound system can be rapidly determined using logarithms if the gain of each stage is known on a logarithmic basis.