Question

Study the image given below, identify A, B, C and D and select the correct option.

• A. A – Negatively charged wire, B – Negatively charged dust particles, C – Discharge corona, D – Collection plate
• B. A – Negatively charged wire, B – Discharge corona, C – Collection plate, D – Negatively charged dust particles
• C. A – Positively charged wire, B – Positively charged dust particles, C – Discharge corona, D – Collection plate
• D. A – Positively charged wire, B – Discharge corona, C – Collection plate, D – Positively charged dust particles

Answer 1

The correct option is B A – Negatively charged wire, B – Discharge corona, C – Collection plate, D – Negatively charged dust particles

Electrostatic precipitators are devices used to remove air pollutants that are particulate in nature, from the exhaust of thermal power plants. These devices are capable of removing 99 % of the particulate matter present in the exhaust.

An electrostatic precipitator consists of negatively charged electrode wires (A) that are maintained at several thousand volts for producing a discharge corona (B). The corona releases electrons which coat the dust particles and render them a net negative charge.

Grounded collecting plates with positive charge (C) are present to attract the negatively charged dust particles (D). This causes the dust particles to settle down and separate out from the exhaust being passed through the precipitator.

The velocity of air between the collecting plates is maintained low in order to allow the dust to fall. These dust particles are collected and removed. Clean air from the electrostatic precipitator is let out to the smokestack (a chimney or funnel for discharging smoke) which is later released into the atmosphere. Hence option b is correct.

Figure: Diagrammatic representation of electrostatic precipitator