An electric dipole is placed at an angle of 30∘ with an electric field intensity 2×105N/C. It experiences a torque equal to 4N-m. The charge on the dipole, if the dipole length is 2cm is
A
4μC
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B
2mC
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C
2μC
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D
4mC
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Solution
The correct option is B2mC Given: E=2×105N/C;τ=4N-m l=2cm=2×10−2m
Torque experienced by a dipole placed in uniform electric field is →τ=→p×→E
The magnitude of torque will be
τ=pEsinθ
⇒τ=(ql)Esinθ
⇒q=τlEsinθ
⇒q=42×10−2×2×105×12
∴q=2×10−3C=2mC
Hence, option (b) is correct.
Why this question?Tip: The torque acting on dipole is always ⊥rto plane of →Eand dipole moment vector (→P).