Clarify your elementary notions about current in a metallic conductor by answering the following queries :
(a) The electron drift speed is estimated to be only a few `mm s^(-1)` for currents established almost the instant a circuit is closed?
(b ) The electron drift arises due to the force experienced by electons in the electric field inside the conductor. But force should cause acceleation. Why then do the electrons acquire a steady drift speed?
( c )If the electron drift speed is so small, and electron's charge is small, how can we still obtain large amounts of current in a conductor?
(d ) 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 ?
(e ) Are the paths of electons straight lines between successive collisions (with the positive ions of the metal ) in the (i) absence of electic filed, (ii) presence of electic field.
Clarify your elementary notions about current in a metallic conductor by answering the following queries :
(a) The electron drift speed is estimated to be only a few `mm s^(-1)` for currents established almost the instant a circuit is closed?
(b ) The electron drift arises due to the force experienced by electons in the electric field inside the conductor. But force should cause acceleation. Why then do the electrons acquire a steady drift speed?
( c )If the electron drift speed is so small, and electron's charge is small, how can we still obtain large amounts of current in a conductor?
(d ) 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 ?
(e ) Are the paths of electons straight lines between successive collisions (with the positive ions of the metal ) in the (i) absence of electic filed, (ii) presence of electic field.
(a) The electron drift speed is estimated to be only a few `mm s^(-1)` for currents established almost the instant a circuit is closed?
(b ) The electron drift arises due to the force experienced by electons in the electric field inside the conductor. But force should cause acceleation. Why then do the electrons acquire a steady drift speed?
( c )If the electron drift speed is so small, and electron's charge is small, how can we still obtain large amounts of current in a conductor?
(d ) 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 ?
(e ) Are the paths of electons straight lines between successive collisions (with the positive ions of the metal ) in the (i) absence of electic filed, (ii) presence of electic field.
Text Solution
Verified by Experts
(a) When we close the circuit, the electric field is set up in the entire closed circuit instantly with the speed of eleectromagnetic wave which causes electron drift at every portion of the circuit. Due to it, the current so set up in the entire circuit instantly. The current so set up does not wait for the electrons to flow from one end of the conductor to other end. However, the current does take a little time to reach its steady value.
( b) When a potential difference is applied across the ends of a conductor, the electric field is set up inside the conductor. Due to it, each free electron in the conductor experiences a force and is accelerated towards the positive end of the conductor, resulting in the increase in its speed until it collides with a positive ion of the metal. After the collision, the free electorn loses its speed but again starts to accelerate by virute of force on it due to electric field. Its speed inceraess again only to suffer a collision again and so on. Therfore, on the average, the free electrons acquire only a drift speed in the conductor, under the effect of electic field.
( c) In a conductor, we obtain large amount of current even if the electorn drift speed is small and electron's charge is small, because the electron number density in the conductor is very large, (of the order of `10^(29) m^(-3)`).
(d) When a potential difference is applied across the ends of a conductor, the drifting of free electrons takes place from lower to higher potential. These drifiting electrons also have thermal velocity. At an instant, each free electron moves in a direction of resultant velocity of its thermal velocity and drift velocity, which is different for various free electrons in a conductor. Hence, all the free electrons in the metal conductor are not moving in the same direction.
(e) (i) In the absence of electric field, the paths of electrons are straight lines between successive collisions with positive ions of the metal, since the electrons are moving with their thermal velocity like molecules in a gas.
(ii) In the presence of electric field, the paths of the electrons between two successive collisisons with positive ions are curved as each electron is having two velocities (a) thermal velocity and (b) velocity by virtue of force due to electic field.
( b) When a potential difference is applied across the ends of a conductor, the electric field is set up inside the conductor. Due to it, each free electron in the conductor experiences a force and is accelerated towards the positive end of the conductor, resulting in the increase in its speed until it collides with a positive ion of the metal. After the collision, the free electorn loses its speed but again starts to accelerate by virute of force on it due to electric field. Its speed inceraess again only to suffer a collision again and so on. Therfore, on the average, the free electrons acquire only a drift speed in the conductor, under the effect of electic field.
( c) In a conductor, we obtain large amount of current even if the electorn drift speed is small and electron's charge is small, because the electron number density in the conductor is very large, (of the order of `10^(29) m^(-3)`).
(d) When a potential difference is applied across the ends of a conductor, the drifting of free electrons takes place from lower to higher potential. These drifiting electrons also have thermal velocity. At an instant, each free electron moves in a direction of resultant velocity of its thermal velocity and drift velocity, which is different for various free electrons in a conductor. Hence, all the free electrons in the metal conductor are not moving in the same direction.
(e) (i) In the absence of electric field, the paths of electrons are straight lines between successive collisions with positive ions of the metal, since the electrons are moving with their thermal velocity like molecules in a gas.
(ii) In the presence of electric field, the paths of the electrons between two successive collisisons with positive ions are curved as each electron is having two velocities (a) thermal velocity and (b) velocity by virtue of force due to electic field.
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If the electron drift speed is so small and the electron's charge is small, how can we still obtain large amounts of current in a conductor ?
The electron drift arises due to the force experienced by electrons in the electric field inside the conductor. But force should cause acceleration. Why then do the electrons acquire a steady average drift speed ?
Knowledge Check
The electron drift speed is small and the charge of the electron is also small but still , we obtain large current in a conductor . This is due to the
The electron drift speed is small and the charge of the electron is also small but still , we obtain large current in a conductor . This is due to the
A
Conducting property of the conductor
B
Resistance of the conductor is small
C
Electron number density of the conductor is small
D
Electron number density of the conductor is enomous
Electric current is due to drift of electrons in
Electric current is due to drift of electrons in
A
Metallic conductors
B
Semi-conductors
C
Both (a) and (b)
D
None of these
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(a) In Example 3.1, the electron drift speed is estimated to be only a few mm s^(-1) for currents in the range of a few amperes? How then is current established almost the instant a circuit is closed? (b) The electron drift arises due to the force experienced by electrons in the electric field inside the conductor. But force should cause acceleration. Why then do the electrons acquire a steady average drift speed? (c) If the electron drift speed is so small, and the electron’s charge is small, how can we still obtain large amounts of current in a conductor? (d) 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? (e) Are the paths of electrons straight lines between successive collisions (with the positive ions of the metal) in the (i) absence of electric field, (ii) presence of electric field?
If the electron drift speed is so small (~ 10 ^(-3) m//s) and the electron’s charge is very small, how can we still obtain a large amount of current in a conductor.
The electron drift speed is estimated to be only a few mm s^(-1) for currents in the range of a few amperes. How then is current established almost the instant a circuit is closed ?
Electron drift speed is estimated to be only a few mm/s for currents in the range of few amperes ? How then is current established almost the instant a circuit is closed.
Electron drift speed is estimated to be of the order of mm s^(-1) . Yet large current of the order of few amperes can be set up in the wire. Explain briefly.
The drift speed of an electron in a metal is in the order of