I was reading an article about working of ESP at this website:


enter image description here

Though the explanation was nice, I couldn't understand what the diagram conveys.

Anyone who can help with the meaning of the diagram on this page?


Looks like two positively charged plates with negatively charged rods spaced apart in between. Air flows in, corona discharge strips the air molecules of electrons which ionizes them, and the free electrons bounce around and hit the dust particles and negatively charge them. The now negatively charged dust particles are attracted to the positive plates out of the air.

Both plates are positive because it's a lot easier to charge the dust negatively than it is to charge it postively. You want to maximize surface area to attract the dust and the maximum surface area is from the plates. So the plates are positively charged. The negative electrodes need to be narrow to promote coronal discharge (by concentrating the electric field like a lightning rod). Since the negative eletrodes can't attracting dust anyways, the narrower the better.

The coronal discharge produces free-electrons by stripping the air of electrons thereby ionizing it, and the free electrons stick to the dust particles thereby negatively charging them.

  • \$\begingroup\$ Why have they shown negative charge on both electrodes? \$\endgroup\$ – programmer Feb 5 at 6:32
  • 1
    \$\begingroup\$ @programmer they haven't. the outer plates are shown as +ve. \$\endgroup\$ – Brian Drummond Feb 5 at 13:51
  • \$\begingroup\$ @programmer Look again. The plates are postively charged and are attracting negatively charged dust particles onto them. \$\endgroup\$ – DKNguyen Feb 5 at 14:56
  • \$\begingroup\$ How come both the plates are positive? \$\endgroup\$ – programmer Feb 6 at 10:09
  • \$\begingroup\$ @programmer the top and bottom structures are the cross section of the same electrode, the pipe that is used as positive electrode. The negative electrodes are inside. Sometimes it's a wire inside a pipe. \$\endgroup\$ – Sredni Vashtar Feb 6 at 17:11

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.