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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Electric Field and Potential

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Electric Field and Potential

The electric potential in a region of space is given by V(x, y, z)...

The electric potential in a region of space is given by V(x,y,z)=A(xy+yz+zx)V(x, y, z) = A(xy + yz + zx). Given that AA is 1010 SI units, determine the magnitude of the electric field at the point (1 m,1 m,1 m)(1 \text{ m}, 1 \text{ m}, 1 \text{ m}).

Options

  1. A303 N C−130\sqrt{3} \text{ N C}^{-1}
  2. B203 N C−120\sqrt{3} \text{ N C}^{-1}
  3. C103 N C−110\sqrt{3} \text{ N C}^{-1}
  4. D10 N C−110 \text{ N C}^{-1}

Correct answer

B. 203 N C−120\sqrt{3} \text{ N C}^{-1}

Step-by-step solution

The electric field E⃗\vec{E} is related to the electric potential VV by the negative gradient of the potential:

E⃗=−(∂V∂xi^+∂V∂yj^+∂V∂zk^)\vec{E} = -\left( \dfrac{\partial V}{\partial x}\hat{i} + \dfrac{\partial V}{\partial y}\hat{j} + \dfrac{\partial V}{\partial z}\hat{k} \right)

Given V(x,y,z)=A(xy+yz+zx)V(x, y, z) = A(xy + yz + zx) and A=10A = 10, we have:

Ex=−∂V∂x=−A(y+z)E_x = -\dfrac{\partial V}{\partial x} = -A(y + z)

Ey=−∂V∂y=−A(x+z)E_y = -\dfrac{\partial V}{\partial y} = -A(x + z)

Ez=−∂V∂z=−A(x+y)E_z = -\dfrac{\partial V}{\partial z} = -A(x + y)

Substituting x=1x = 1, y=1y = 1, z=1z = 1 and A=10A = 10:

Ex=−10(1+1)=−20E_x = -10(1 + 1) = -20

Ey=−10(1+1)=−20E_y = -10(1 + 1) = -20

Ez=−10(1+1)=−20E_z = -10(1 + 1) = -20

The electric field vector is E⃗=−20i^−20j^−20k^\vec{E} = -20\hat{i} - 20\hat{j} - 20\hat{k}.

The magnitude of the electric field is:

∣E⃗∣=(−20)2+(−20)2+(−20)2=400+400+400=1200=203 N C−1|\vec{E}| = \sqrt{(-20)^2 + (-20)^2 + (-20)^2} = \sqrt{400 + 400 + 400} = \sqrt{1200} = 20\sqrt{3} \text{ N C}^{-1}
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