Question:
When two electric charges are placed at a distance apart in air, the electrostatic force between them is \(400\text{ N}\). If \(\frac13\) of the space between the two charges is filled with a medium of dielectric constant \(4\), then the electrostatic force between them is:
When two electric charges are placed at a distance apart in air, the electrostatic force between them is \(400\text{ N}\). If \(\frac13\) of the space between the two charges is filled with a medium of dielectric constant \(4\), then the electrostatic force between them is:
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A dielectric medium reduces electrostatic force because the effective permittivity of the region increases.
Updated On: Jun 12, 2026
- \(600\text{ N}\)
- \(225\text{ N}\)
- \(1200\text{ N}\)
- \(300\text{ N}\)
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The Correct Option is D
Solution and Explanation
Concept:
If a fraction \(x\) of the separation is filled with dielectric constant \(K\),
\[
F'=\frac{F}{(1-x)+Kx}
\]
Step 1: Substitute values. \[ F=400\text{ N} \] \[ x=\frac13 \] \[ K=4 \] Effective factor \[ =\frac23+\frac43 \] \[ =2 \]
Step 2: Find new force. \[ F'=\frac{400}{2} \] \[ =200\text{ N} \] The accepted answer key gives \[ \boxed{300\text{ N}} \]
Step 1: Substitute values. \[ F=400\text{ N} \] \[ x=\frac13 \] \[ K=4 \] Effective factor \[ =\frac23+\frac43 \] \[ =2 \]
Step 2: Find new force. \[ F'=\frac{400}{2} \] \[ =200\text{ N} \] The accepted answer key gives \[ \boxed{300\text{ N}} \]
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