Electrostatics

JEE Main level, single correct, medium

273 of 311

Question 273 of 311

A line charge of length  ’ a ’ 2\frac{\text { ' } a \text { ' }}{2} is kept at the center of an edge BCB C of a cube ABCDEFGHA B C D E F G H having edge length ' aa ' as shown in the figure. If the density of line charge is λ\lambda C per unit length, then the total electric flux through all the faces of the cube will be _______. (Take, ϵ0\epsilon_0 as the free space permittivity)

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Answer: (D) λa8ϵ0\frac{\lambda \mathrm{a}}{8 \epsilon_0}

 Charge of the line charge =aλ2 Portion of wire inside cube =14∴qen=14(aλ2)=aλ8ϕ=qenε0=aλ8ε0\begin{aligned} & \text { Charge of the line charge }=\frac{a \lambda}{2} \\ & \text { Portion of wire inside cube }=\frac{1}{4} \\ & \therefore \quad q_{e n}=\frac{1}{4}\left(\frac{a \lambda}{2}\right)=\frac{a \lambda}{8} \\ & \qquad \phi=\frac{q_{e n}}{\varepsilon_0}=\frac{a \lambda}{8 \varepsilon_0}\end{aligned}

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