A pendulum bob of mass 30mg carrying a charge of 2.0×10−8 is at rest in a uniform horizontal electric field of 20000N/C. The tension in the thread of the pendulum is (g=10m/s2):
A
5×10−4N
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B
4×10−4N
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C
3×10−4N
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D
2×10−4N
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Solution
The correct option is C5×10−4N HorizontalforceactingonCharge=qE=2×10−8×20000
FH=4×10−4N
Verticalforceactingoncharge=mg=30×10−6×10=3×10−4N
Tension will be equal to resultant of electrostatic force and force due to gravity,