Two large, parallel conducting plates X and Y, kept close to each other, are given charges Q1 and Q2(Q1>Q2). The four surfaces of the plates are A, B, C and D, as shown in figure. Then :
A
The charge on A is 12(Q1+Q2).
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B
The charge on B is 12(Q1−Q2).
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C
The charge on C is -12(Q1−Q2).
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D
The charge on D is 12(Q1+Q2)
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Solution
The correct options are A The charge on B is 12(Q1−Q2). B The charge on A is 12(Q1+Q2). C The charge on C is -12(Q1−Q2). D The charge on D is 12(Q1+Q2) Let charge for surface A =Q1−q, for surface B =q, for surface C =Q2−q′ and for surface D =q′. As the field inside X plate is zero, 12Aϵ0(Q1−q−q−Q2+q′−q′)=0 −2q=Q2−Q1⇒q=12(Q1−Q2) similarly for Y plate, 12Aϵ0(q′−Q2+q′−q−Q1+q)=0 or 2q′=Q1+Q2⇒q′=12(Q1+Q2) Thus, charge on A is Q1−q=Q1−12(Q1−Q2)=12(Q1+Q2). charge on B is q=12(Q1−Q2) charge on C is Q2−q′=Q2−12(Q1+Q2)=−12(Q1−Q2) Charge on D is q′=12(Q1+Q2)