Classify charge interactions and calculate charge flow.
Method and worked examples
Objects become charged when electrons transfer or redistribute; their protons remain bound in nuclei during ordinary charging. Like charges repel and unlike charges attract. Metals contain mobile electrons, while ions carry current in electrolytes. Charge is conserved: it is transferred rather than consumed. A conductor allows charge to move readily; an insulator restricts that motion.
Current is charge passing a point per second: I=tQ, with amperes A, coulombs C and seconds s. Rearrange before substituting and convert milliseconds to seconds. Conventional current follows positive-charge motion, opposite electron drift in a metal. In a steady unbranched circuit, equal charge passes each point each second.
Example 1
A charge of 18C passes in 6.0s. Find current.
I=tQ=6.018=3.0A.
Example 2
How much charge passes a wire carrying 0.25A for 2.0 minutes?
t=120s. Q=It=0.25×120=30C.
Watch out:A lamp transfers electrical energy. Charge is conserved, so steady current entering and leaving it is equal.
6. Charge and electric current | Year 11 Physics | Ascent Arcade