A cube of side a has point charges +Q located at each of its vertices except at the origin where the charge is -Q. The electric field at the centre…
JEE Main 2021 — Physics Electromagnetism
2021mcqmedium
A cube of side a has point charges +Q located at each of its vertices except at the origin where the charge is −Q. The electric field at the centre of cube is:
Official previous-year question
Held on 24 Feb 2021 · Verified 6 Jul 2026.
Options
A
33πϵ0a2−Q(x^+y^+z^)
B
33πϵ0a2Q(x^+y^+z^)
C
33πϵ0a2−2Q(x^+y^+z^)
D
33πϵ0a22Q(x^+y^+z^)
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Solution
We can replace −Q charge at origin by +Q and −2Q.
Now due to +Q charge at every corner of cube. Electric field at center of cube is zero so now net electric field at center is only due to −2Q charge at origin.
E=r3kqr=4πϵ0(2a3)31(−2Q)2a(x^+y^+z^)
E=33πa2ϵ0−2Q(x^+y^+z^)
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