Question

1. Why is there an electric field in a wire carrying a current if the wire is a conductor?

2. Which is easier and why, inserting a dielectric into a charged capacitor that is either connected or not connected to a battery?

3. Describe the motion of electrons moving through a conductor.

Answer 1

1. When a conductor is placed in an external static electric field then free electrons inside conductors moves on the surface of conductors and this movement continues till electric field generated by these electrons cancels the external electric field. And electric field inside wire becomes zero.

Now when we apply a potential difference across a conductor, then we connect the conductor by a battery or something else. then the electric field will accelerate electrons and these electrons will start passing through battery and will reach the other end of conductor and this process will continue. Earlier the conductor was placed in electric field and not connected a to it. Therefore electrons moves on the surface but couldn't go further.

2. When a dielectric is inserted inside an isolated capacitor , one that is not connected to battery. Then since the charge on capacitor is fixed , electric field inside dielectric goes down. Therefore it is easier to introduce dielectric slab in an unconnected capacitor.

When we introduce a dielectric slab in a connected charged capacitor then electric inside remains same because the decrease in electric field is compensated by battery by providing extra charged. Thus by increasing charges on plates of capacitor electric field is maintained same. Thus it is difficult to insert a slab in a capacitor connected to a battery.

3. If the conductor is not connected to an external source of potential difference then the net flow of electrons will be zero. Electrons will move randomly inside the conductor due to thermal energy of electrons. And average current will be zero. But when a potential difference is applied to a conductor then each electron experience a net force along with the random thermal motion. Due to this now electrons starts drifting in the conductor. That is their path no longer remains random. Thus current flows inside conductor.