Charging capacitor - no resistor

In summary: However, for the average person, this is a beyond the scope of this class. In summary, the student is correct in reasoning that the p.d across the capacitor is equal to the emf of the source. The student is incorrect in reasoning that the p.d across the resistor will decrease until the p.d across the capacitor equals the p.d source.
  • #1
jsmith613
614
0

Homework Statement



When charging a capacitor with NO resistor in the circuit, the p.d of the capacitor IMMIDIATELY reaches a maximum...

CapacitorQ.png


Homework Equations


The Attempt at a Solution



...is the following reasoning correct:

As stated by Kirchoff's Law, the sum of the potential differences across all components in a series circuit is equivalent to the the emf of the source...as there are no other compoenents in the circuit the p.d across the capacitor = emf of source immediatley.

(Note: when a resistor is present the p.d across the resistor decreases intil the p.d across capacitor = p.d source)

Is this correct?
 
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  • #2
jsmith613 said:

Homework Statement



When charging a capacitor with NO resistor in the circuit, the p.d of the capacitor IMMIDIATELY reaches a maximum...

CapacitorQ.png


Homework Equations





The Attempt at a Solution



...is the following reasoning correct:

As stated by Kirchoff's Law, the sum of the potential differences across all components in a series circuit is equivalent to the the emf of the source...as there are no other compoenents in the circuit the p.d across the capacitor = emf of source immediatley.

(Note: when a resistor is present the p.d across the resistor decreases intil the p.d across capacitor = p.d source)

Is this correct?

I like your reasoning - but would like to see some reference to the idea that you have been instructed to assume the resistance of the wires is zero, and thus regardless of current flow, the p.d across them will be zero, and then an explanation that if real wires were used, their tiny resistance would mean a very short charge time, rather than an instantaneous charging.

Peter
 
  • #3
PeterO said:
I like your reasoning - but would like to see some reference to the idea that you have been instructed to assume the resistance of the wires is zero, and thus regardless of current flow, the p.d across them will be zero, and then an explanation that if real wires were used, their tiny resistance would mean a very short charge time, rather than an instantaneous charging.

Peter

this was a question I made up myself based on a diagram in my book
thanks so much, through, for confirming my reasoning :)
 
  • #4
You are also leaving out the internal resistance of the power source. There is no such thing as a totally ideal power source.
 
  • #5
Also, any wire, no matter the resistance, has some inductance. Between that and the results of attempting to drive an infinite current (requiring infinite speed for finite charge carriers) you've left the realm of normal circuit theory and entered Maxwell's and Einstein's domain. Happy adventuring :smile:
 
  • #6
The circuit as posed is not a physics problem but a circuit theory problem. The battery has zero internal resistance as do the wires. Assuming you switch the discharged capacitor onto the battery you will have an infinite current for an infinitesimal time as the capacitor charges. The math can be handled by the theory of distributions, aka delta functions.
 

1. What is a charging capacitor with no resistor?

A charging capacitor with no resistor is a circuit where a capacitor is connected directly to a power source without a resistor in the circuit. This allows for a quick charging of the capacitor, but can also lead to potential damage to the capacitor or power source if not done properly.

2. How does a charging capacitor with no resistor work?

In a charging capacitor with no resistor, the capacitor acts as a short-term storage for electrical energy. As soon as it is connected to a power source, the capacitor begins to charge until it reaches the same voltage as the power source. This process is fast because there is no resistor to limit the flow of current. However, without a resistor, the capacitor can quickly reach dangerous levels of voltage and potentially damage the circuit.

3. What are the dangers of using a charging capacitor with no resistor?

The main danger of using a charging capacitor with no resistor is the risk of overcharging. Without a resistor to limit the flow of current, the capacitor can quickly reach high levels of voltage and potentially cause damage to the circuit or even start a fire. Additionally, the sudden release of energy from a fully charged capacitor can also be dangerous for anyone handling the circuit.

4. Can a charging capacitor with no resistor be used in any circuit?

No, a charging capacitor with no resistor should only be used in specific circuits where the voltage and current are carefully controlled. In most cases, a resistor is necessary to protect the capacitor and the rest of the circuit from damage. It is important to consult with an experienced engineer or scientist before using a charging capacitor with no resistor in a circuit.

5. How can the risks of using a charging capacitor with no resistor be mitigated?

The risks of using a charging capacitor with no resistor can be mitigated by carefully calculating the voltage and current in the circuit and choosing a capacitor with the appropriate voltage rating. Additionally, using a multimeter to monitor the voltage of the capacitor during charging can help prevent overcharging. It is also important to have a clear understanding of the circuit and seek guidance from an expert if needed.

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