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Charge on particle must be negative as then it will experience force in upward direction balancing the mg force due to its weight. Therefore, mg=qE ( q is charge on particle, only magnitude, and E is electric field)
The magnitude of an electric field in which the electric force on a proton is equal in magnitude to its weight = E
E =1.0228756*10^-7 N/C
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Jan 18th, 2016
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