Fluid filled sacs in the knee are specifically called Bursa or Bursae. Bursae is plural for Bursa.
A bursa is a closed fluid filled sac that function as a gliding surface to reduce friction between tissues of the body. Knee bursitis occurs when there is irritation or inflammation in one one of the knee bursa. The procedure of removing fluid-filled sac is called bursectomy. When the bursa become infected with bacteria, this condition is called septic bursitis.
The sun, diamond mines, the air we breathe, labs, steel factories.
I believe the statement would be that, A magnetic field created by the electric current causes the compass needle to move.
An electric current through a conductor creates a magnetic field,such that when a charged particle such as an electron, proton, or ion is in motion, magnetic lines of force rotate around the particle. Since current moving through the wire consists of electrons in motion, there is a magnetic field around the wire, which causes the compass needle to deflect.
