Q. 1

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



A. The speed of he electron is more at B than at A.

B. The electric current is from left to right.

C. The magnitude of the current is larger at B than at A.

D. The current density is more at B than at B.

Answer :

Electric field is in the direction form right to left.

Let velocity of an electron at stop A is


velocity of an electron at stop A is


Potentials are increased in the opposite direction of electric field.


So


Potential energy of the electron at point A is



Potential energy of the electron at point B is




Because


Kinetic energy of an electron at point A is


Kinetic energy of an electron at point B is


Applying conservation of mechanical energy , we get



(Mechanical energy =potential energy+kinetic energy)


(Because


Speed of electron is more at stop B than stop A. Option A is correct.

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