Electric charge is the property of a particle that causes it to produce an electric field and to experience a force when placed in another electric field. Charge can be either positive or negative. Opposite charges (+ & -) will feel a force of attraction whilst like charges (+ & + or - & -) will feel a force of repulsion.
The unit of electric charge is the coulomb, C. A proton or an electron carry the smallest amount of charge possible, known as the elementary charge, e. e = 1.6 x 10^-19 C Therefore an electron carries charge -e and a proton carries charge + e Charge is quantised. That is, that it comes in lumps (it is not continuous). The smallest amount of charge we can have is 1.6x10^-19 C and the total (or net) charge on a particle or object must be a multiple of e. So the quantity of charge = 2.4x10^-19C does not exist! We can only have total charges of Ne, where N = an integer. (e.g. e, 2e, 3e, 4e... etc...) Current Electric Current is the rate of flow of charge. So, I = Q/t (often we see delta Q / delta t i.e. current is the change in charge over the change in time) It is from this equation that we define the unit of charge. The coulomb is defined as the quantity of charge that passes a point when a current of 1 A flows for 1 second. So 1 C = 1 As The constituents of current In a metal it is the electron movement that makes up the current However, in an electrolyte (a conducting liquid) it is the ions that make up the current We usually define the direction of current as the direction of positive charge flow - this is known as 'conventional current' in a circuit the electrons will flow from the negative terminal to the positive - this is known as 'electron flow' (and is in the opposite direction to conventional current - however, remember that negative charge flowing one way is exactly the same as positive charge flowing in the opposite direction) Comments are closed.
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