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Class 12 › Physics › Electric Charge and Field
CBSE2024Class Class 12 · Physics2 Marks · Short✅ Verified
Two point charges +2 µC and +4 µC repel each other with a force of 20 N. If a charge of −6 µC is added to each of them, what is the new electrostatic force?
✅ Answer & Solution
<b>Given:</b><br>• q<sub>1</sub> = +2 µC, q<sub>2</sub> = +4 µC<br>• Initial force F = 20 N (repulsive)<br>• Charge added = -6 µC to each<br><br><b>Step 1: Find new charges</b><br>q<sub>1</sub>' = +2 + (-6) = <b>-4 µC</b><br>q<sub>2</sub>' = +4 + (-6) = <b>-2 µC</b><br><br><b>Step 2: Compare products of charges</b><br>Initial product: q<sub>1</sub> × q<sub>2</sub> = 2 × 4 = +8 (µC)²<br>New product: q<sub>1</sub>' × q<sub>2</sub>' = (-4) × (-2) = +8 (µC)²<br><br><b>Step 3: Apply Coulomb's Law</b><br>F ∝ |q<sub>1</sub> × q<sub>2</sub>|/r²<br><br>Since:<br>• Magnitude of product remains the same<br>• Distance r remains unchanged<br><br><b>Magnitude of force does not change:</b> F' = 20 N<br><br><b>Step 4: Determine nature of force</b><br>Both new charges are <b>negative</b> (same sign), so force is <b>repulsive</b>.<br><br><b>Final Answer:</b><br><b>New force = 20 N (repulsive)</b>
