A neutron is thought to be composed of one “up” quark of charge and two “down” quarks each having charge . If the down quarks are apart inside the neutron, we have to calculate the repulsive electrical force between them.

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Charge of a down-quark is where .

It is given that the separation between the two down-quarks inside a neutron is . Therefore, the magnitude of the force of repulsion between the two down-quarks inside a neutron will be