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A system of three charges are placed as shown in the figure : +q d –q D Q , If D >> d, the potential energy of the system is best given by :

1. 0 4 1 ∈ π ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ + + 2 2 D qQd d q
2. 0 4 1 ∈ π ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ 2 2 D qQd – d q –
3. 0 4 1 ∈ π ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ + 2 2 D qQd 2 d q –
4. 0 4 1 ∈ π ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ 2 2 D 2 qQd – d q –

Correct answer: 0 4 1 ∈ π ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ 2 2 D qQd – d q –

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