CBSE Class 12 Physics 2019 Delhi Set 2 Paper

Question : 5

Total: 6

(a) Draw equipotential surfaces corresponding to the electric field that uniformly increases in magnitude along with the Z-direction.
(b) Two charges −q and +q are located at point (0,0,−a) and (0,0,a). What is the electrostatic potential at the points (0,0,±z) and (x,y,0) ?

Solution:

(a)

Vz‌=‌

(z−a)

+‌

k(−q)

(z+a)

‌ if ‌z>a
‌=Kq[‌

z−a

−‌

z+a

]=Kq‌

z2−a2

Potential at pt. (0,0−z)
V(−z)‌=‌

(z−a)

+‌

K(−q)

(z+a)

‌=Kq[‌

z−a

−‌

z+a

]
‌=Kq‌

z2−a2

∵r for the point is √x2+y2+a2
∴‌‌V(x,y,0)‌=‌

(x2+y2+a2)1∕2

+‌

K(−q)

(x2+y2+a2)1∕2

‌=0.

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