Andifit's horizontallyplanepolarised, wecanalsodenotethiswith a horizontalarrowtoshowthattheelectromagneticfieldortheparticlesareoscillatinginthehorizontaldirection.
Assoonasitreacheswhatisknownas a polarisingfilter, thecomponentwhichisoscillatinginthehorizontaldirectionwillbeabsorbedandonlylightwhichisoscillatingintheverticalplanewillpassthroughthepolarisingfilter.