FOLLOW US ON TWITTER
SHARE THIS PAGE ON FACEBOOK, TWITTER, WHATSAPP ... USING THE BUTTONS ON THE LEFT


YOUR PARTICIPATION FOR THE GROWTH OF PHYSICS REFERENCE BLOG

Saturday, April 18, 2020

The electric potentials V are measured at distances x from P along a line PQ. The results are


Question 29
The electric potentials V are measured at distances x from P along a line PQ. The results are
V / V               13                    15                    18                    21                    23
x / m                0.020               0.030               0.040               0.050               0.060

The component along PQ of the electric field for x = 0.040 m is approximately
A 75 Vm-1 towards P.
B 300 Vm-1 towards Q.
C 300 Vm-1 towards P.
D 450 Vm-1 towards Q.
E 450 Vm-1 towards P.





Reference: Past Exam Paper – J78 / II / 22





Solution:
Answer: C.

The electric potential at a point is defined as the work done per unit positive charge in moving a small test charge from infinity to the point. At infinity, the electric potential is defined to be zero.


The electric field strength E is related to the potential gradient ΔV/Δx as follows:

Electric field strength: E = – ΔV / Δx


We want to find the electric field strength at x = 0.040 m. So, we need to consider values of potential around this point.

Concerned points (V, x): (15, 0.030), (18, 0.040) and (21, 0.050)

The distance are being measured from point P. So, the smaller the value of x, the closer it is to P.


EITHER
E = – ΔV / Δx                             
E = – (18-15) / (0.040-0.030) = – 300 V m-1

OR
E = – ΔV / Δx
E = – (21-18) / (0.050-0.040) = – 300 V m-1


The negative sign in the value of the electric field strength E indicates that E is in the direction of decreasing x.

The values of x are smaller closer to P. So, the direction is towards P.

No comments:

Post a Comment

If it's a past exam question, do not include links to the paper. Only the reference.
Comments will only be published after moderation

Currently Viewing: Physics Reference | The electric potentials V are measured at distances x from P along a line PQ. The results are