Two concentric uniformly charged spherical shells both carry positive charge. With point B lying between the shells (or appropriately positioned) and C farther out, choose the correct statement.

Electric field magnitude at B may be greater than that at C.
Electric field magnitude at B must be greater than that at C.
Potential at A is greater than potential at B.
If a charge moves from B to C the work done by the electric force must be positive.

Correct answer: Electric field magnitude at B may be greater than that at C.

Solution

For concentric positively charged shells, the field depends on which shells' charge each point encloses and on distance. The relative magnitudes at B and C depend on the charge values and radii, so the field at B can be greater than at C in some cases but is not guaranteed. Hence 'may be greater' is correct; 'must be' is too strong.

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