Problem 20(5.oo points) A He ion is moving towards a proton (p) as shown in the

Question

Problem 20(5.oo points) A He ion is moving towards a proton (p) as shown in the figure. The position of the proton is fixed. The dashed circles represent the equipotential surfaces around the proton and the electric potentials for each surface are shown in the figure. Initially, the He2 ion is so far away from the proton so that the electric potential at that point is essentially equal to zero. The initial kinetic energy of the He ion is 20 eV. Which of the following correctly describes the motion of the He+ ion: (Note: charge for He-ion = +3.2x10", C; charge of proton = +1.6x1019 C, i eV. 1.6 x10s ) 10V 20 V He A) It will stop at point A and it will be bounced back B) It will stop at point B and it will be bounced back C) It will stop at point C and it will be bounced back D) It will not stop until it touches the proton E) Insufficient information to determine at which point the He ion will stop.

Explanation / Answer

Initial KE of He ion = 20eV,

At nearest point, KE will be zero and potential energy will be maximum, i.e. equal to initial KE.

It means maximum potential energy He ion can have is 20eV.

maximum potential = PE/q

= 20eV/2e as charge of He2+ is 2e or two times electron's charge but positive

= 10V

option A is correct

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