13.10 Applications of electrostatics  (Page 3/14)

Smoke precipitators and electrostatic air cleaning

Another important application of electrostatics is found in air cleaners, both large and small. The electrostatic part of the process places excess (usually positive) charge on smoke, dust, pollen, and other particles in the air and then passes the air through an oppositely charged grid that attracts and retains the charged particles. (See [link] .)

Large electrostatic precipitators    are used industrially to remove over 99% of the particles from stack gas emissions associated with the burning of coal and oil. Home precipitators, often in conjunction with the home heating and air conditioning system, are very effective in removing polluting particles, irritants, and allergens.

Integrated concepts

The Integrated Concepts exercises for this module involve concepts such as electric charges, electric fields, and several other topics. Physics is most interesting when applied to general situations involving more than a narrow set of physical principles. The electric field exerts force on charges, for example, and hence the relevance of Dynamics: Force and Newton’s Laws of Motion . The following topics are involved in some or all of the problems labeled “Integrated Concepts”:

• Kinematics
• Two-Dimensional Kinematics
• Dynamics: Force and Newton’s Laws of Motion
• Uniform Circular Motion and Gravitation
• Statics and Torque
• Fluid Statics

The following worked example illustrates how this strategy is applied to an Integrated Concept problem:

Acceleration of a charged drop of gasoline

If steps are not taken to ground a gasoline pump, static electricity can be placed on gasoline when filling your car’s tank. Suppose a tiny drop of gasoline has a mass of $4.00\times {10}^{\mathrm{–15}}\text{kg}$ and is given a positive charge of $3.20\times {10}^{\mathrm{–19}}\text{C}$ . (a) Find the weight of the drop. (b) Calculate the electric force on the drop if there is an upward electric field of strength $3.00\times {10}^5\text{N/C}$ due to other static electricity in the vicinity. (c) Calculate the drop’s acceleration.