Find out the following
a. `V_A - V_B`
b. `V_B - V_C`
c. `V_C - V_A`
d. `V_D - V_C`
e. `V_A - V_D`
f. Arrange the order of potential for points (A, B,C and D).
.

Explanation

(i) The potential difference between two points in electric field is
`|Delta V_(AB)| = - vec E . vec(AB) = E d cos theta = E. d`
=`E d = 20 xx 2 xx 10^(-2) = 0.4`
So `V_A - V_B = 0.4 V`
Negative because in the direction of electric field, potential always decreases.
(ii) `|Delta V_(BC) | = E d = 20 xx 2 xx 10^(-2) = 0.4`
d is the distance between the equipotential passing through
B and C, so `V_B - V_C = 0.4 V`
(iii) `|Delta V_(CA) | = E d = 20 xx 4 xx 10^(-2) = 0.8`
So `V_C - V_A = -0.8 V`
Negative because in the direction of electric field, potential always decreases.
(iv) `|Delta V_(DC) | = E d = 20 xx 0 = 0`
So `V_D - V_C = 0`
Because the effective distance between D and C is zero. Also potential difference between C and D is zero as both the points lie on same equipotential.
(v) `|Delta V_(A D)| = Ed = 20 xx 4 xx 10^(-2) = 0.8`
Here d is the distance between equipotential pasing through A and D.
So `V_A - V_D = 0.8 V`
Because in the direction of electric field, potential always decreases.
(vi) The order of potential is
`V_A gt V_B gt V_C = V_D`.