The lower-case letter i symbolizes instantaneous current, which means the amount of current at a specific point in time. This stands in contrast to constant current or average current (capital letter I) over an unspecified period of time. The expression dv/dt is one borrowed from calculus, meaning the instantaneous rate of voltage change over time,. In this equation we see something novel to our experience thus far with electric circuits: the variable of time. When relating the quantities of voltage, current, and resistance to a resistor, it doesnt matter if were dealing with measurements taken over an unspecified period of time (E=IR; V=IR), or at a specific moment in time (e=ir; v=ir). The s. When mathematics students first study calculus, they begin by exploring the concept of rates of change for various mathematical functions. The derivative, which is the first and most elementary calculus principle, is an expression of one variables rate of change in terms of another. Calculus students have to learn this principle while studying abst. Again, the amount of current through the capacitor is directly proportional to the rate of voltage change across it. The only difference between the effects of a decreasing voltage and an increasing voltage is the direction of current flow. For the same rate of voltage change over time, either increasing or decreasing, the current magnitude (amps).