capacitor and inductor

Consider energy

 

An inductor creates a magnetic field. A capacitor creates an electrostatic field. Energy is stored in the field. What causes the strength of the field to increase in each case?

 

I don't understand the question. In the capacitor by itself, the rate of change in voltage is proportional to the current. If you want a spike of voltage across the cap, then you have to apply a step of current. Perhaps you can give an example of what you mean. Everything takes a finite amount of time to change. Instantaneous is theoretical.

Ratch

 

If dE/dt = I/C , then no current means the voltage holds steady. A large fast step of current increases the voltage rapidly until the current drops back to zero. Then the cap voltage will hold at new larger value.

Ratch

 

If I/C is a step that means that I/C goes from zero to some constant value instantaneously. That means that dE/dt goes from zero to some constant value. But a constant dE/dt means the voltage slope is a constant which is the same as saying that the voltage is a ramp. I don't believe that a voltage ramp can be called a spike.

 

Nothing happens instantaneously in the real world. If a step voltage occurs in a capacitor, then a current spike occurs. When does a voltage stop being a ramp and start to be a step in the physical world?

Ratch

 

So which statement is correct?

 

In #3 I suggested consider energy.
If the capacitor is to be increased in voltage, it will need to be supplied with energy. To raise the voltage instantaneously it will need infinite power. This is not available here.

 

The second statement. Sorry for the confusion.

Ratch