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JEE Advanced 2023Paper 2
Exam
JEE Advanced
Year
2023
Paper
Paper 2
Subject
Physics
Chapter
Electrostatics

JEE Advanced 2023 · Paper 2 · Physics · Electrostatics

An electric dipole is formed by two charges + q and - q located in...

An electric dipole is formed by two charges +q+ q and −q- q located in xyxy-plane at (0,2)mm( 0, 2 ) mm and (0,−2)mm( 0, - 2 ) mm, respectively, as shown in the figure. The electric potential at point P(100,100)mmP ( 100, 100 ) mm due to the dipole is V0{V}_{0}. The charges +q+ q and –q– q are then moved to the points (−1,2)mm( - 1, 2 ) mm and (1,−2)mm( 1, - 2 ) mm, respectively. What is the value of electric potential at PP due to the new dipole?

An electric dipole is formed by two charges + q and - q located in xy -plane at ( 0, 2 ) mm and ( 0, - 2 ) mm ,

Options

  1. AV04\dfrac{{V}_{0}}{4}
  2. BV02\dfrac{{V}_{0}}{2}
  3. CV02\dfrac{{V}_{0}}{\sqrt{2}}
  4. D3V04\dfrac{3{V}_{0}}{4}

Correct answer

B. V02\dfrac{{V}_{0}}{2}

Step-by-step solution

Electric potential at any general point for vertical dipole is written as, V1∝p1cosθ1(r1)2{V}_{1} ∝ \dfrac{{p}_{1}cos{\theta}_{1}}{{\left({r}_{1}\right)}^{2}}.

An electric dipole is formed by two charges + q and - q located in xy -plane at ( 0, 2 ) mm and ( 0, - 2 ) mm ,

Electric potential at any general point for V2∝p2cosθ2(r2)2{V}_{2} ∝ \dfrac{{p}_{2}cos{\theta}_{2}}{{\left({r}_{2}\right)}^{2}}.

An electric dipole is formed by two charges + q and - q located in xy -plane at ( 0, 2 ) mm and ( 0, - 2 ) mm ,

For first case:

tanθ1=100100=1⇒θ1=45°tan{\theta}_{1} = \dfrac{100}{100} = 1 ⇒ {\theta}_{1} = 45 °

For second case:

slope in this is =−2−21−(−1)=−2= \dfrac{- 2 - 2}{1 - \left(- 1\right)} = - 2

which is equal to

tan⁡(45°+θ2)=−2⇒1+tanθ21−tanθ2=−2⇒1+tanθ2=−2+2tanθ2⇒tanθ2=3cosθ2=132+12=110\tan \left(45 ° + {\theta}_{2}\right) = - 2 ⇒ \dfrac{1 + tan{\theta}_{2}}{1 - tan{\theta}_{2}} = - 2 ⇒ 1 + tan{\theta}_{2} = - 2 + 2tan{\theta}_{2} ⇒ tan{\theta}_{2} = 3cos{\theta}_{2} = \dfrac{1}{\sqrt{{3}^{2} + {1}^{2}}} = \dfrac{1}{\sqrt{10}}

also r1=r2{r}_{1} = {r}_{2}.

Therefore, required ratio

V2V1=p2cosθ2p1cosθ1\dfrac{{V}_{2}}{{V}_{1}} = \dfrac{{p}_{2}cos{\theta}_{2}}{{p}_{1}cos{\theta}_{1}}

V2V1=ql2×110ql1×12=(2−(−2))2+(−1−1)24×5=254×5=12\dfrac{{V}_{2}}{{V}_{1}} = \dfrac{q{l}_{2} \times \dfrac{1}{\sqrt{10}}}{q{l}_{1} \times \dfrac{1}{\sqrt{2}}} = \dfrac{\sqrt{{\left(2 - \left(- 2\right)\right)}^{2} + {\left(- 1 - 1\right)}^{2}}}{4 \times \sqrt{5}} = \dfrac{2\sqrt{5}}{4 \times \sqrt{5}} = \dfrac{1}{2}

⇒V2=V02⇒ {V}_{2} = \dfrac{{V}_{0}}{2}

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