Which of the following statement(s) is/are correct? The work done by the external force in moving [2011]

Question

Which of the following statement(s) is/are correct? [2011]

Smart Achievers · Accepted Answer

(3, 4)

(1) Gauss's law is valid only when $E \propto r^{- 2} .$

(2) Gauss's law cannot be used to calculate the field distribution around an electric dipole.

(3) (3) is correct, as between two point charges we will get a point where the electric field due to the two point charges cancels out each other. If two point charges are of opposite sign, then the two fields are along the same direction; hence they cannot be zero.

(4) $W_{A B} = q (Δ V) = 1 (V_{B} - V_{A})$ or, $W_{A B} = V_{B} - V_{A} .$

Solution

Q.
Which of the following statement(s) is/are correct [2011]

1 If the electric field due to a point charge varies as $r^{- 2.5}$ instead of $r^{- 2}$ , then the Gauss law will still be valid.

2 The Gauss law can be used to calculate the field distribution around an electric dipole.

3 If the electric field between two point charges is zero somewhere, then the sign of the two charges is the same.

4 The work done by the external force in moving a unit positive charge from point $A$ at potential $V_{A}$ to point $B$ at potential $V_{B}$ is $(V_{B} - V_{A})$ .

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