Quick conceptual question about disconnecting battery

In summary, if a parallel plate capacitor is connected to a battery and then disconnected, the voltage will be zero but the charge (Q) will remain the same. This is because a capacitor stores charges and they cannot simply disappear. In order to calculate the work needed to insert a dielectric, the original charge of the capacitor is used. This is because the charge remains in the capacitor even when the battery is disconnected. Additionally, the capacitor will maintain a voltage according to Q = C*V, even without an external voltage source applied. However, if the capacitance changes, the voltage will also change if the charges have nowhere to go.
  • #1
xchococatx
7
0
If there is a parallel plate capacitor, connected to a battery, which is then disconnected, there is NO voltage now, but "Q" (charge) on the capacitor remains the same. YES OR NO? I think yes.
 
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  • #2
xchococatx said:
If there is a parallel plate capacitor, connected to a battery, which is then disconnected, there is NO voltage now, but "Q" (charge) on the capacitor remains the same. YES OR NO? I think yes.

What is your reasoning?
 
  • #3
Well basically I'm thinking that a capacitor stores charges (or energy) so, onces its all charged up by a battery, I don't see how it could lose those charges...even when the battery is disconnected. (immediately anyways, it wouldn't be all gone I don't think) Why I was thinking about this was because if the battery is now disconnected, and you wanted to calculate the work needed to insert a dielectric, fitting perfectly between the 2 plates, since there is no voltage, I don't see how you could calculate the work unless you used the original charge of the capacitor (without dielectric). (By means of E=Q^2/2C) So in order to use the original charge of the capacitor, I figured charge has to stay in the capacitor even if the battery is disconnected.
 
  • #4
xchococatx said:
Well basically I'm thinking that a capacitor stores charges (or energy) so, onces its all charged up by a battery, I don't see how it could lose those charges...even when the battery is disconnected. (immediately anyways, it wouldn't be all gone I don't think) Why I was thinking about this was because if the battery is now disconnected, and you wanted to calculate the work needed to insert a dielectric, fitting perfectly between the 2 plates, since there is no voltage, I don't see how you could calculate the work unless you used the original charge of the capacitor (without dielectric). (By means of E=Q^2/2C) So in order to use the original charge of the capacitor, I figured charge has to stay in the capacitor even if the battery is disconnected.

Okay, your reasoning is pretty good. Note that the charged capacitor will maintain a voltage (potential difference) according to Q = C*V, even without an external voltage source applied. Of course, if the capacitance changes (due, say, to the insertion of a dielectric) the voltage will change accordingly if the charges have nowhere to go.
 
  • #5


Yes, your understanding is correct. When a battery is disconnected from a parallel plate capacitor, the voltage across the capacitor drops to zero, but the charge on the capacitor remains the same. This is because the charge on a capacitor is stored on the plates and is not affected by the presence or absence of a voltage source. The charge will only change if there is a change in the capacitance or if the capacitor is discharged.
 

FAQ: Quick conceptual question about disconnecting battery

Why is it important to disconnect the battery before working on a vehicle?

Disconnecting the battery before working on a vehicle is important for safety reasons. It reduces the risk of electrical shock or short circuits, which can cause serious injury or damage to the vehicle.

How do I disconnect the battery properly?

To disconnect the battery properly, start by turning off the engine and removing the keys from the ignition. Then, locate the negative (-) terminal and use a wrench to loosen and remove the negative cable from the terminal. Repeat the same process for the positive (+) terminal. Make sure to secure the cables away from the battery to prevent accidental reconnection.

Do I need to disconnect the battery to change a fuse or light bulb?

No, you do not need to disconnect the battery to change a fuse or light bulb. However, it is recommended to disconnect the negative cable as an extra precaution to avoid any potential electrical issues.

Can disconnecting the battery reset the car's computer?

Yes, disconnecting the battery can reset the car's computer. This can sometimes be helpful in resolving minor issues with the vehicle's performance. However, it can also cause the car's radio, clock, and other settings to reset, so it is not recommended unless necessary.

How often should I disconnect the battery to check its condition?

It is not necessary to disconnect the battery to check its condition. Instead, you can use a multimeter to measure the voltage and determine if the battery needs to be replaced. If the battery has been disconnected for a long period of time, it may need to be recharged before testing its condition.

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