Doubly ionized helium nuclei (charge ) are accelerated from rest through an electric…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Doubly ionized helium nuclei (charge +2e) are accelerated from rest through an electric potential difference of 3.0 kV. Immediately afterward they enter a region where a uniform electric field opposes their motion, producing a potential change of magnitude ∣△Vd∣ designed to slow the nuclei to a speed of 1.0×105ms−1 before they leave the apparatus. Non-electric forces are negligible.
(a) Calculate the speed of the helium nuclei just before they enter the decelerating region.
(b) Determine the magnitude ∣△Vd∣ of the decelerating potential difference required to reach the specified final speed.
(c) Describe qualitatively how changing the sign of △Vd (so that it assisted rather than opposed the motion) would affect the exit speed of the nuclei, and explain why.