Questions in physics.....?

Question

1- Why do you change the unit of time constant from sec tp min in charging the capacitor expirament?

2- Explain: when we connect on series electrical lamb with capacitor and DC current we fined the lambis lightening for few time then it stops, but when we connect it with AC current the lamb id lightening very well and for a long time?

Answer 1

1. No one does that. Why would they do that?

2. Series and parallel circuits.

In he series circuit (where battery, capacitor, lamp are connected to each other in a head to tail fashion) the current flow until the capacitor is charged to the level of supply voltage, than the current stops flowing and lamp turns off

In parallel circuit (where battery, capacitor, lamp are connected to each other in a head-to-had, tail-to-tail fashion) at first the capacitor has zero voltage and as it starts to charge the voltage also grows across the lamp and it becomes brighter and brighter.

Answer 2

1. I don't know about this either.

2. I think Edward misunderstood, thinking your 2nd condition was parallel.

Quick summary of capacitor operation. Capacitors conduct very high frequency AC voltage with very little impedance. When you first turn the DC on, the capacitor sees the voltage change and passes it on. But a DC voltage is blocked after a brief time.

More detail:

If the + side of a battery is connected to one plate of the cap, electrons leave that plate rushing towards the battery, so the plate is positively charged. The opposite plate then attracts electrons from the circuit on that side of the cap, the lamp in your case. This is a current that appears to flow through the cap. But understand that electrons do not cross the gap between the plates. After a short time, the second plate has sucked all the electrons it can from the lamp. The battery voltage will appear across the capacitor ternminals, an equilibrium has been achieved and current stops

With AC The polarity on the first plate keeps changing so the electrons keep rushing toward the voltage source and back towards the cap. The other plate then is first attracting and then repelling electrons. Electrons do not cross the gap between the plates in AC case either. This will continue as long as the instantaneous voltage at the AC source keeps changing.