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प्रश्न
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.
विकल्प
The speed of the electrons is more at B than at A
The electric current is from left to right
The magnitude of the current is larger at B than at A
The current density is more at B than at A
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उत्तर
The speed of the electrons is more at B than at A
Let the potentials at A and B be VA and VB.
As potential,
\[E = - \frac{dV}{dr}\]
potential increases in the direction opposite to the direction of the electric field.
Thus, VA < VB
Potential energy of the electrons at points A and B:-
UA = -eVA
UB = -eVB
Thus, UA > UB
Let the kinetic energy of an electron at points A and B be KA and KB respectively.
Applying the principle of conservation of mechanical energy, we get:-
UA + KA = UB + KB
As, UA > UB,
KA < KB
Therefore, the speed of the electrons is more at B than at A.
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संबंधित प्रश्न
Define the term drift velocity.
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(B) Free-electron density in a metal depends on temperature.
Thomson Effect is caused _______________ .
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Define relaxation time.
Consider two conducting wires A and B of the same diameter but made of different materials joined in series across a battery. The number density of electrons in A is 1.5 times that in B. Find the ratio of the drift velocity of electrons in wire A to that in wire B.
Two conductors, made of the same material have equal lengths but different cross-sectional areas A1 and A2 (A1 > A2). They are connected in parallel across a cell. Show that the drift velocities of electrons in two conductors are equal.
The drift velocity of electrons in a conductor connected to a battery is given by vd = `(−"eE" τ)/"m"`. Here, e is the charge of the electron, E is the electric field, τ is the average time between collisions and m is the mass of the electron.
Based on this, answer the following:
- How does the drift velocity change with a change in the potential difference across the conductor?
- A copper wire of length 'l' is connected to a source. If the copper wire is replaced by another copper wire of the same area of cross-section but of length '4l', how will the drift velocity change? Explain your answer.
What is the average time interval between two successive collisions of a free electron with the ions of the metallic lattice called?
Which symbol denotes relaxation time?
What is current density?
If \[n\] is the number of free electrons per unit volume and \[A\] is the conductor’s cross-sectional area, which expression gives the current from electron drift?
Which expression gives current density in terms of free electron density, relaxation time, and electric field?
