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प्रश्न
Two point charges qA = 3 μC and qB = −3 μC are located 20 cm apart in vacuum.
- What is the electric field at the midpoint O of the line AB joining the two charges?
- If a negative test charge of magnitude 1.5 × 10−9 C is placed at this point, what is the force experienced by the test charge?
उत्तर
a. Electric fields at O due to the charges at A and B are
`E_(OA) = E_(OB) = 1/(4 pi ε_0) q/r^2`
`9 xx 10^9 xx (3 xx 10^-6 "C")/((20/(2 xx 10^-2 m)^2))`
or EOA = EOA = 27 × 105 NC-1
Being in the same direction results in a net electric field at the midpoint O, which is
E = EOA + EOB
= 2EOB
= 2 × 27 × 105
or E = 5.4 × 106 N C-1 directed along OB.
b. A force acts onto the test charge when it is put at point O, with q0 = −1.5 × 10-9 C.
F = q0E
= 1.5 × 10-9 × 5.4 × 106
or F = 8.1 × 10-3 N
Along OA, which is opposite to E.
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