Question

What is meant by drift speed of free electrons?

Answer 1

• There are always some free electrons inside any metal at room temperature .There will be some free electrons. these free electron inside the move randomly and collide frequently with heavier atoms and change their direction of motion at every time.When a steady electric field is applied to conductor, the electrons start moving towards the positive terminal of applied electrical potential difference but this movement of electrons doesn't happen in straightway. During travelling towards the positive potential the electrons continuously collide with the atoms and bounced back in a random fashion. During the collision the electrons lose some of their kinetic energy and again due to the presence of electric field, they are re-accelerated towards the positive potential and regain their kinetic energy. Again, during further collision the electrons partly lose their kinetic energy in the same manner. Thus the applied electric field cannot stop the random motion of the electrons inside a conductor. Although in presence of applied electric field, the motion of the electrons is still random, but there will be over all resultant movement of electrons towards positive terminals. In other words, the applied electric field makes the electrons to drift towards positive terminal. That means the electrons get an average drift velocity.
• drift velocity is denoted by $u$,
• $u={\mu }_{e}E=\frac{I}{nAQ}$