AP EAMCET201824 Apr 2018Morning ShiftPhysicsElectrostaticsActual
When a soap bubble of radius 0.2 ~mm is charged, it experiences an outward electrostatic pressure of magnitude ^2 2 ₀ , where =20 Cm ⁻² is the surface charge density. If the excess pressure inside the soap bubble due to the surface tension is same as this electrostatic pressure, then the surface tension of the soap solution is ( ₀=8.85 10⁻¹² C ^2 ~N ⁻¹ ~m ⁻² )
Options
- A8.85 10⁻⁴ Nm ⁻¹
- B12.4 10⁻⁴ Nm ⁻¹
- C11.3 10⁻⁴ Nm ⁻¹
- D90 10⁻⁴ Nm ⁻¹
Correct answer
C. 11.3 10⁻⁴ Nm ⁻¹
Step-by-step solution
Excess pressure inside soap bubble due to surface tension, p= ( 4 S R ) , where S= surface tension and R= radius. Electrostatic pressure, p= ^2 2 ₀ According to the question, 4 S R = ^2 2 ₀ Putting all values in Eq. (i), we get aligned & S= (20 10⁻⁶ )^2 (0.2 10⁻³ ) (8 8.85 10⁻¹² ) & S=11.3 10⁻⁴ ~N / m aligned