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Question
A particle of mass 1 g and charge 2.5 × 10−4 C is released from rest in an electric field of 1.2 × 10 4 N C−1. Find the electric force and the force of gravity acting on this particle. Can one of these forces be neglected in comparison with the other for approximate analysis?
Solution
Given:
Charge of the particle, q = 2.5 × 10−4 C
Initial velocity, u = 0
Electric field intensity, E = 1.2 × 104 N/C
Mass of the particle, m = 1 g = 10−3 kg
Distance travelled, s = 40 cm = 4 × 10−1 m
Electric force,
\[F_e = qE\]
\[ \Rightarrow F_e = 2 . 5 \times {10}^{- 4} \times 1 . 2 \times {10}^4 = 3 \] N
Force of gravity,
\[F_g = \text{ mg }\]
\[ \Rightarrow F_g = 9 . 8 \times {10}^{- 3} \] N
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