JEE Mains · Physics · STD 12 - Electric potential and capacitance
- JEE Mains 2026
- Medium
- MCQ
The electric potential as a function of \(x, y\) is given by \(V = 5(x^2 - y^2)\) V. The electric field at a point \((2, 3)\) m is __________ V/m.
Pick an option to check your answer.
Answer & Solution
Correct Answer
(A) \((-20\hat{i} + 30\hat{j})\)
Step-by-step Solution
Detailed explanation
The electric field \(\vec{E}\) is given by the negative gradient of the electric potential \(V\):
\(\vec{E} = -\left( \dfrac{\partial V}{\partial x} \hat{i} + \dfrac{\partial V}{\partial y} \hat{j} \right)\)
Given \(V = 5(x^2 - y^2)\), we find the partial derivatives:
\(\dfrac{\partial V}{\partial x} = 10x\)
\(\dfrac{\partial V}{\partial y} = -10y\)
Substituting these into the expression for \(\vec{E}\):
\(\vec{E} = -(10x \hat{i} - 10y \hat{j}) = -10x \hat{i} + 10y \hat{j}\)
At the point \((2, 3)\), substitute \(x = 2\) and \(y = 3\):
\(\vec{E} = -10(2) \hat{i} + 10(3) \hat{j} = -20\hat{i} + 30\hat{j}\) V/m
Answer: \((-20\hat{i} + 30\hat{j})\)
\(\vec{E} = -\left( \dfrac{\partial V}{\partial x} \hat{i} + \dfrac{\partial V}{\partial y} \hat{j} \right)\)
Given \(V = 5(x^2 - y^2)\), we find the partial derivatives:
\(\dfrac{\partial V}{\partial x} = 10x\)
\(\dfrac{\partial V}{\partial y} = -10y\)
Substituting these into the expression for \(\vec{E}\):
\(\vec{E} = -(10x \hat{i} - 10y \hat{j}) = -10x \hat{i} + 10y \hat{j}\)
At the point \((2, 3)\), substitute \(x = 2\) and \(y = 3\):
\(\vec{E} = -10(2) \hat{i} + 10(3) \hat{j} = -20\hat{i} + 30\hat{j}\) V/m
Answer: \((-20\hat{i} + 30\hat{j})\)
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