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39. (a)
Gujarat State Board of School Textbooks, Textbook of Physics (Part-I) (Std. XII), pp 169-17 (Chapter 7 on Electrical Currents) "In this chapter we will study the effects associated with motion of electric charges. Moving charges constitution the electric currents.
To the Negative Terminal of Battery
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Jain Educationa International
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Direction of the field in the conductor
"Suppose a conductor is connected to the terminals of a battery as shown in fig. To understand the process occurring in the conductor microscopically, we should first understand the internal structure of a metalic conductor. In a metalic substance, the valence electrons of the constituent atoms do not remain attached to their respective parent atoms, but get detached, leaving the atoms as ions. The ions so formed, are arranged at specific locations forming a geometric pattern known as a crystal lattice. The 'free' electrons move in the space between the ions in a random fashion, which for convenience is shown by a line in fig. In absence of an external electric field, if we consider any cross-section across the conductor, the number of electrons crossing it in all directions are equal. Hence net flow of electrons across the cross-section is zero which means there is zero current.
Now when such a conductor is connected to the terminals of a battery as shown in the fig. an electric field is set up in the conductor and electrons experience a force acting towards the positive terminals of the battery. Under the influence of this force, the electrons acquire a drift towards the positive terminal which is superposed on their random velocity, e.g. an electron which moved from A to B in a given time, now moves from A to B' in the same time. The drift experienced by it during this time is B', and one can now define an appropriate drift velocity.
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To the Positive Terminal of Battery
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