Question:

 A vertical electric field of magnitude 4.9 × 105 N/C just prevents a water droplet of a mass of 0.1 g from falling. The value charge on the droplet will be(Given g = 9.8 m/s2)

Updated On: Sep 24, 2024
  • 1.6 × 10–9 C

  • 2.0 × 10–9 C

  • 3.2 × 10–9 C

  • 0.5 × 10–9 C

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The Correct Option is B

Solution and Explanation

Since the droplet is at rest
⇒ Net force = 0
⇒ mg = qE
⇒ q=\(\frac{mg}{E}\)=2×10-9 C
The correct option is (B) :  2.0 × 10–9 C

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Concepts Used:

Electric Field

Electric Field is the electric force experienced by a unit charge. 

The electric force is calculated using the coulomb's law, whose formula is:

\(F=k\dfrac{|q_{1}q_{2}|}{r^{2}}\)

While substituting q2 as 1, electric field becomes:

 \(E=k\dfrac{|q_{1}|}{r^{2}}\)

SI unit of Electric Field is V/m (Volt per meter).