Drift of Electrons and the Origin of Resistivity

Derive an expression for  drift velocity of free electrons.

A conductor of length ‘l’ is connected to a dc source of potential ‘V’. If the length of the conductor is tripled by gradually stretching it, keeping ‘V’ constant, how will (i) drift speed of electrons and (ii) resistance of the conductor be affected? Justify your answer.

Consider the following statements.
(A) Free-electron density is different in different metals.
(B) Free-electron density in a metal depends on temperature.

Peltier Effect is caused _______________ .

When electrons drift in a metal from lower to higher potential, does it mean that all the free electrons of the metal are moving in the same direction?

Explain the term ‘drift velocity’ of electrons in conductor. Hence obtain the expression for the current through a conductor in terms of ‘drift velocity’. 

1. Consider circuit in figure. How much energy is absorbed by electrons from the initial state of no current (ignore thermal motion) to the state of drift velocity?
2. Electrons give up energy at the rate of RI² per second to the thermal energy. What time scale would one associate with energy in problem (a)? n = no of electron/volume = 10²⁹/m³, length of circuit = 10 cm, cross-section = A = (1mm)²

Estimate the average drift speed of conduction electrons in a copper wire of cross-sectional area 1.0 × 10⁻⁷ m² carrying a current of 1.5 A. Assume the density of conduction electrons to be 9 × 10²⁸ m⁻³

Electrons are emitted by a hot filament and are accelerated by an electric field, as shown in the figure. The two stops at the left ensure that the electron beam has a uniform cross-section.