Five equally spaced points along the -axis in a vacuum are labeled P ( ), Q ( ), R (…

PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences

Problem

Five equally spaced points along the

x

-axis in a vacuum are labeled P (

x=0\,\text{cm}

), Q (

x=2\,\text{cm}

), R (

x=4\,\text{cm}

), S (

x=6\,\text{cm}

), and T (

x=8\,\text{cm}

). The electric potential at each point is listed below:

Point	Potential (V)
P	+90
Q	+50
R	+5
S	-40
T	-70

Two particles are released simultaneously from rest at point Q and travel only along the

+x

direction: • Particle A: charge

+3e

• Particle B: charge

-2e

(The elementary charge magnitude is

e = 1.60\times10^{-19}\,\text{C}

.) Assume no forces other than electrostatic act on either particle. (a) Determine the electric potential difference between points Q and S. (b) Calculate the change in electric potential energy of particle A when it moves from Q to S. (c) Calculate the change in electric potential energy of particle B over the same displacement and compute the ratio

\Delta U_B / \Delta U_A

. (d) Explain the physical significance of the signs of

\Delta U_A

and

\Delta U_B

in terms of energy transfer between each particle and the electric field.

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