isiGwinqa siyindawo emkhathingeni lapho unyanta unamandla kangangokuba akukho okwazi ukuphunyuka noma ukuphuma kuso, ngisho iziHoyana/izinhlayiyana noma iMiyonzi yomHonyazi ("electromagnetic radiation") njengokukhanya uqobo azikwazi ukuphumela esiGwinqeni. Umngcele lapho kungaphunyukwa khona wesiGwinqa ubizwa ngoMkhawulo wesiGwinya. Isigwinqa siyinkanyezi ese ike iqhunyiwe ekufeni, saze isisindo sayo saqala ukuhudula konke kuso isigwinqa.