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Two particles A and B having charges 20 μC and -5 μC respectively are held fixed with a separation of 5 cm. At what position should a third charged particle be placed so that it does not experience a net electric force? 20μC A —— 5 cm —— B -5μC

1. At 5 cm from 20 μC on the left side of system
2. At 5 cm from -5 μC on the right side of system
3. At 1.25 cm from -5 μC between two charges
4. At midpoint between two charges

Correct answer: At 5 cm from -5 μC on the right side of system

Solution

The third charged particle must be placed where the electric forces from both charges balance each other. At 5 cm from the -5 μC charge on the right side, the attractive force from the -5 μC charge and the repulsive force from the 20 μC charge will equalize, resulting in no net force on the third particle.

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