How Does a Capacitor React to a Sawtooth Wave Input?

  • Thread starter vig
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In summary, a capacitor has resistance and inductance, and these elements limit the current that can flow into the capacitor. So an instantaneous change in voltage across a capacitor will not result in an infinite current.
  • #1
vig
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Capacitor---very basic questions

Ive already gone through many posts on working of capacitors...but if i consider a very simple circuit...say i connect a function generator (which generates a sawtooth wave) across a capacitor...(no resistance in series)...and i measure voltage across the capacitor, what will be the waveform like?..one theory says that since the capacitor is connected in parallel to the function generator, i must get the same sawtooth waveform..however, voltage across capacitor can not change abruptly and so i should be getting a smooth waveform across it..it would be great if someone can clear things out...:smile:
 
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  • #2


If it is an ideal voltage generator, and an ideal capacitor, the voltage generator will supply the infinite current necessary to get an abrupt change in the voltage across the capacitor. In practice, both the capacitor and the voltage generator have some resistance and some inductance, and the voltage generator is limited in the amount of current it can supply. These non-ideal elements will determine exactly what the waveform looks like.
 
  • #3


'voltage generator will supply the infinite current necessary to get an abrupt change in the voltage across the capacitor'...could u pls elaborate on this?..and considering the most ideal situation, the waveform across a capacitor would show sharp peaks??...and if a resistor is connected in series, and the function generator can still source infinite current (say), the waveform would remain the same?
 
  • #4


vig said:
'voltage generator will supply the infinite current necessary to get an abrupt change in the voltage across the capacitor'...could u pls elaborate on this?..
The current into a capacitor is proportional to the rate of change of the voltage across the capacitor. An instantaneously abrupt change in voltage represents an infinitely large rate of change for the voltage, therefore the current would have to be infinite to produce such a voltage change across a capacitor.
and considering the most ideal situation, the waveform across a capacitor would show sharp peaks??...
Yes, in this idealized and very impossible scenario physguy described, that is exactly what would happen. (Ignoring that pesky detail about it being impossible.)
and if a resistor is connected in series, and the function generator can still source infinite current (say), the waveform would remain the same?
No, a resistor limits the current that an ideal voltage source would produce.
 
  • #5


Redbelly98 said:
The current into a capacitor is proportional to the rate of change of the voltage across the capacitor. An instantaneously abrupt change in voltage represents an infinitely large rate of change for the voltage, therefore the current would have to be infinite to produce such a voltage change across a capacitor.

Yes, in this idealized and very impossible scenario physguy described, that is exactly what would happen. (Ignoring that pesky detail about it being impossible.)

No, a resistor limits the current that an ideal voltage source would produce.

so very crudely speaking...its not a capacitor's fault that it does not allow a sharp change in voltage..it is essentially the inability of the source to provide an infinite current?...
 
  • #6


vig said:
so very crudely speaking...its not a capacitor's fault that it does not allow a sharp change in voltage..it is essentially the inability of the source to provide an infinite current?...

Suppose I'm trying to fill a swimming pool. Would you say, "It's not the swimming pool's fault that it doesn't fill up immediately, it's my inability to find a big enough hose!"?
 
  • #7


vig said:
so very crudely speaking...its not a capacitor's fault that it does not allow a sharp change in voltage..it is essentially the inability of the source to provide an infinite current?...
Not quite. A real capacitor has some resistance, as do the connecting wires. And any closed circuit has a nonzero inductance too. So there are several factors at play that limit the current.

If we spent more time thinking about how real devices behave, we might come up with other factors too.
 
  • #8


phyzguy said:
Suppose I'm trying to fill a swimming pool. Would you say, "It's not the swimming pool's fault that it doesn't fill up immediately, it's my inability to find a big enough hose!"?
Is'nt it true?..if u could get a big hose then the swimming pool would fill up immediately..:uhh:
 

1. What is a capacitor?

A capacitor is an electronic component that stores electrical energy in an electric field. It is made up of two conductive plates separated by an insulating material, known as a dielectric.

2. How does a capacitor work?

A capacitor works by storing electric charge on its plates. When a voltage is applied across the capacitor, one plate accumulates positive charge while the other accumulates negative charge. The dielectric material between the plates prevents the charges from flowing together, thus storing the energy.

3. What are the types of capacitors?

There are various types of capacitors, including ceramic, electrolytic, film, and variable capacitors. They differ in their materials, construction, and performance characteristics, and are used for different purposes based on their properties.

4. How are capacitors used in electronic circuits?

Capacitors have a wide range of applications in electronic circuits. They are commonly used for filtering, decoupling, and energy storage. They can also be used in timing circuits, voltage regulators, and signal coupling.

5. How do I choose the right capacitor for my circuit?

When choosing a capacitor for a circuit, factors such as capacitance, voltage rating, and temperature stability should be considered. The type of capacitor and its size can also affect its performance. It is best to consult a datasheet or seek advice from an electronics expert for specific circuit requirements.

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