Electric charge is the pheesical property o matter that causes it tae experience a force when close tae ither electrically charged matter. Thare are twa types o electric charges – positive an negative. Positively charged substances are repelled frae ither positively charged substances, but attracted tae negatively charged substances; negatively charged substances are repelled frae negative an attractit tae positive. An object will be negatively charged if it haes an excess o electrons, an will itherwise be positively charged or uncharged. The SI derived unit o electric charge is the coulomb (C), altho in electrical ingineerin it is an aa common tae uise the ampere-hour (Ah), an in chemistry it is common tae uise the elementary charge (e) as a unit. The seembol Q is eften uised tae denote a charge. The study o hou charged substances interact is classical electrodynamics, which is accurate insofar as quantum effects can be ignored.